General Knowledge Reference Manual
Unit Components: ............................................................................................................... 2
Daily Engine Inspection and Maintenance ....................................................................... 13
Rig-up ............................................................................................................................... 19
Well Head (Tree) .............................................................................................................. 35
Facilities ............................................................................................................................ 39
Down-hole Information .................................................................................................... 41
Down-Hole Components and Tools.............................................................................. 43
Down-hole Terms ............................................................................................................. 64
Drilling Rigs...................................................................................................................... 94
Fluids............................................................................................................................... 128
ALPHA DRAFT 4-25-2012
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Unit Components:
Triplex Pump
A positive displacement reciprocating pump configured with three plungers that operates
three sets of valves and seats. Triplex pumps are the most common configuration of high
pressure pumps used in both drilling and well service operations and are capable of
handling a wide range of fluid types.
The spring-reinforced, preset packing design of the Tri-plex plunger pump
allows fluid to be pumped smoothly at high pressure. The inlet and discharge valves are
spring-loaded closed and hydraulically opened. At the beginning of the stroke, the
plunger displaces the liquid in the manifold chamber and forces the discharge valve open.
There is a split second at the end of the stroke when both inlet and discharge valves are
closed. As the plunger rod begins its backward stroke, the inlet valve opens to allow more
liquid into the manifold chamber, thereby keeping a smooth forward flow of liquid.
SPM600 LRS Unit 72
SPM600 Diagram
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Power End
Fluid End
Plungers
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The plungers are smooth bore solid displacement cylinders that reciprocate in sequence to
manipulate the inlet and discharge valves in the fluid end of the triplex pump which
enables fluid to be pumped under continuous high pressure.
Valves and Seats
There are two rows of valves and seats. The low pressure feed on the bottom and high
pressure discharge on the top. Each row has three sets of valves and seats. They are
spring loaded in the closed position and actuated by the positive displacement of the
plungers.
Pump Oiler
The pump oiler is an important component in the triplex pump as its function is to
lubricate all the gears, bearings, and crosshead. It is supplied with what ever current form
of Arctic Gear Lube (AGL) 75W-90 that rests at the bottom of the tri-plex casing sump,
filtered, and sent through oil lines to each respective lubrication point.
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Triplex plunger packing
There are two kinds of packing that we use in LRSI TriPlex pumps. The small bobtail
units #26, 36, and 66, use Teflon rope in their Gardner Denver pumps. All of the other
units (# 32, 38, 40, 42, 44, 46, 58, 60, 62, 64, 66, 68, 70, 72, and Skid units #1 and 2) use
some form spring loaded Kevlar Chevron style packing.
Picture of Unit 64 Chevron Plunger Packing
Pump Cavitation
Cavitations are defined as the phenomenon of the formation of vapor bubbles of a
flowing liquid in a region where the pressure of the liquid falls below its vapor pressure.
Cavitations are usually divided into two classes of behavior: inertial (or transient)
cavitations and non-inertial cavitations. Inertial cavitations is the process where a void or
bubble in a liquid rapidly collapses, producing a shock wave. Such cavitations often
occur in pumps, propellers, impellers, and in the vascular tissues of plants. Non-inertial
cavitations are the process in which a bubble in a fluid is forced to oscillate in size or
shape due to some form of energy input, such as an acoustic field. Such cavitations is
often employed in ultrasonic cleaning baths and can also be observed in pumps,
propellers etc.
Also a condition affecting an operating pump whereby the pump space is not fully
charged with fluid being pumped. This may come from inadequate or restricted supply or
from the introduction of air or gas into the fluid stream. The effects of cavitation depend
on the type of pump. Cavitations cause a reduction in pump efficiency and excessive
wear or damage to pump components.
Load Pump
Every LRS unit in our fleet is equipped with a positive displacement load pump,
Transports included. A load pump pulls fluid from a source to the intake side of the pump
and pushes fluid to its discharge side to its destination by a rotating impeller. They are
also sometimes used to prime the centrifugal (Feed Pump).
The Load Pump is also used for its vacuum effect on emptying the last bit of fluid from a
source or for rigging down connections after a task is complete.
LRSI units use 3
different brands of positive displacement load pumps (Bowie, Roper, and Raven).
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Note: It is imperative to have an open destination for the fluid on the discharge side of
pump. The force of fluid will have the ability to blow out valves or seals if deadheaded.
Bowie Standard Gear Pump
Feed Pump
LRS uses a centrifugal pump to supply fluid to the high pressure triplex pump that is the
mainstay of our hot oil units. A centrifugal pump is one that once it is primed, will throw
fluid to its destination by using a bell shaped rotating vane disk attached to a drive shaft.
This allows fluid to move without pulsation as it spins, and the outlet can be restricted
(dead headed) without damaging the pump. We run two types of centrifugal pumps in
LRSI Hot Oil Units, the Mission and Labour.
Note: The feed pump must be primed to function properly. There are many ways to
achieve prime depending on the plumbing configurations of the different units. Each unit
Operator will have experience in their preferred methods to gain prime depending on
fluid types and maintaining fluid integrity for job scope versus the possibility of frozen
unit plumbing in cold temperatures.
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Centrifugal
Mission Feed Pump
Packing Gland
Packing Gland
A device used to seal around a reciprocating or rotating shaft or spindle. A malleable
packing compound is forced into place by an adjustable packing nut, or similar
arrangement. This enables the seal or packing to be tightened to suit the operating
conditions and allows subsequent adjustment to account for wear and lubrication.
Pressure Relief (Pop-Off) Valve
A Pop-off (relief valve) is a safety device intended to keep any contained system from
over pressuring. Usually by tripping a spring or shear pin set to a prescribed safe level
allowing pressure to be relieved into a lower pressure or non-pressured destination
source.
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Burners
LRSI operates two different Burner systems. The older system is referred to as the
Keyway. The newer system is referred to as the Gen Tex. Both are capable of producing
extremely high BTUs (British Thermal Units).
The Burner Coil Output is manipulated by controls to heat fluids to a variable of
temperatures and rates depending on Unit and Operator experience. For every adjustment
in Magnehelic (air measure), rate (rpm or gear), or fluid temperature (incoming fluid),
there will be adjustments to be made with the other two to control a constant temperature.
There is no written minimum for pump rate while heating through the coils. The variables
involved include the Unit, Coils type, Blower style, the Burner nozzles being used, the
temperature of the incoming fluid. Just to name a few.
When heating, the correct mixture of air to fuel will produce a clean flame. Too much air
will produce a light colored flame. Not enough air will produce a darker flame and
smoke.
Burner (Keyway)
The Keyway system is fed by air regulated pressurized diesel in the burner tanks that is
pushed down the burner fuel line through a filter and into adjustable nozzles that vaporize
and ignite inside the burner chamber. The vaporized diesel is then fed air by a blower
which is capable of creating efficient combustion at extremely high BTUs.
There is no written minimum for pump rate while heating through the coils. The variables
involved include the Unit, Coils type, Blower style, the Burner nozzles being used, the
temperature of the incoming fluid. Just to name a few.
There is no written minimum on the actual Magnehelic pressure needed to start a fire.
Too much air will hamper your efforts to light a fire by blowing out the flame, and not
enough blower air and you will fail to ignite the diesel.
Pictures of Keyway Burner Box Controls
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Picture of Unit 40 Keyway Coils
Burner (Gentex)
The Gen Tech system runs on an adjustable fuel pump that pushes diesel down a fuel line
through a filter and sized replaceable nozzles which vaporize in the burner chamber. The
vaporized diesel is fed air by an adjustable blower which is capable of creating efficient
combustion at extremely high BTUs.
There are minimum air and fuel settings for the Gentex Burner System located in the
LRS Burner Operations SOP that need to be followed.
Burner Compartment
External Burner Jet (Ops Cab)
Burner Gauges
Carbon buildup on Igniter and Jet
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Murphy Gauges / Switches
A "Murphy switch" is an electrical switch that is commonly used in industrial
applications. They are designed to protect an engine or component during certain types of
mechanical failures. An example could be; if the machine's engine loses internal oil
pressure the switch would electronically disconnect the engines fuel supply and shut it
down. They are also used to sense temperature and do the same.
LRSI incorporates Murphy switches in the burner systems as to shut off the fuel supply if
the pressure and or temperature in the heating coils exceeds or does not meet the settings
that the switches are set for. There is a pop out fuse that disconnects the power that closes
the circuit which then shuts down the fuel supply. This allows for the safe operation
while burning in case of inattention or distraction that might cause the unsafe
temperatures covered in LRSI Burner Fluids Standard Operating Procedure
.
The switches are designed and manufactured by Frank W. Murphy MFR. of Tulsa, OK.
Murphy Gauges
LRS Unit ESD Book
An ESD (Emergency Shutdown) Book can be found on each LRS unit. This book shows
an overview of the unit with the volumes of fuel and fuel shut off valves, engine
shutdown switches (internal and external), and the Safety System Process Shutdown
Diagram.
The Process Shutdown diagram sheet illustrates the ESD Panel as the core that can shut
down the unit in an emergency before an evacuation if time allows. They have red covers
over the switches that will protect normal operations in progress, but if needed in an
emergency the guards are cleared by flipping up and the switches can be thrown that will
kill the engine (s) by closing an electrical circuit on the fuel pump (s), the heating coil
fuel shutoff solenoid, and on most units a fire box extinguishing agent of some sort.
Hydraulic Pump
Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or
hydrodynamic.
The hydraulic pump is the component that is responsible for supplying the fluid and
pressure to the other components of the hydraulic system. The power generated by a
hydraulic pump is about ten times more than the capacity of an electrical motor.
There are different types of hydraulic pumps such as vane, gear, and piston pumps, etc,
to name a few.
LRS units (for the most part) are powered with Gear and Piston powered hydraulic
pumps.
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Gear Hydraulic Pump
Radial Piston Hydraulic Pump
Hydraulic Motor
Gear and vane motors are used in simple rotating systems. Their benefits include low
initial cost and high rpm.
A gear motor consists of two gears, the driven gear (attached to the output shaft by way
of a key, etc) and the idler gear. High pressure oil is ported into one side of the gears,
where it flows around the periphery of the gears, between the gear tips and the wall
housings in which it resides, to the outlet port. The gears then mesh, not allowing the oil
from the outlet side to flow back to the inlet side.
A vane motor consists of an outer core housing with an eccentric bore, in which runs a
rotor with vanes in it that slide in and out. The force differential created by the
unbalanced force of the pressurized fluid on the vanes causes the rotor to spin in one
direction.
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Hydraulic Motor
Chiksan / Swivel Joint
A Chiksan fitting is a high pressure articulating hardline used to make connections
adjustable by a rotation and a swivel. A double Chicksen enables an easier rig-up for
spacing and the ability for give, regarding vibrations and pump pulsations during job
operations.
Tank and Plumbing Configurations
LRS pump units are varied in design and component configurations, depending on
manufacturer and generation of construction. Each unit is furnished with a plumbing
diagram located on the Process page in the ESD Book located in each Ops Cab.
Every pump job has one thing in common. There is a source for the fluid to be
moved. And there is a destination. It is imperative to each job performed to follow
this simple rule and trace the path to ensure the valve configuration is correct to
affect the desired results.
Do not solely rely on the diagram. Visually trace the plumbing to gain first hand
knowledge of each unit’s systems. This will help enable your understanding of the
flow paths involved for each procedure desired.
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Daily Engine Inspection and Maintenance
Oil Level Check
Oil is the single most vital fluid for maintaining your vehicle's well being. If it drops
below a safe level or deteriorates to a state of ineffectiveness, your entire drive-train
could be history. It needs to be checked on a regular basis and, since manufacturers know
this, they try to make the process a simple, straightforward task. The oil dipstick will
often be clearly labeled with words like "ENGINE OIL" or "OIL" written on a brightly
colored plastic or metal ring, or on a painted yellow metal ring. Pull on this ring until the
dipstick comes completely and wipe it with a clean rag. Reinsert the dipstick and make
sure it goes all the way in or you will get a false reading. Pull it back out and look closely
to determine the oil level. It should be between the two marks at the end of the dipstick,
often labeled with "add" and "fill." You can also check the oil's color and consistency at
this time to see that it does not contain any small metal flakes and that it has a clear or
medium-brown color. If the oil has a black color, it should probably be changed.
Coolant Check
If oil is number one in the fluid pecking order, water, or coolant, ranks a close second
because of its role as a heat regulator. You will want to check your coolant level as often
as you check the oil. This should be done with the engine off and when the vehicle is
cold if you are opening the actual radiator. This will keep you safe from burns if the
radiator is at operating temperature with positive pressure in the coolant system. Most
late-model engines have an overflow tank (light-colored plastic with a rubber tube going
into its cap) that can be checked to determine coolant level with no chance of scalding,
but even these engines should be cold for an accurate reading. Once again, there will be
marks on the overflow tank, often labeled "MIN" and "MAX," that will make identifying
your coolant level a no-brainer. If you have an older vehicle with no overflow tank, open
the radiator when the engine is completely cold and look inside to check for coolant. It
should be visible just below the radiator opening.
Miscellaneous Fluid and Battery Check:
With oil and coolant out of the way, you've covered the most crucial aspects of vehicle
maintenance. Now all that's left is a general fluid check and battery check. As with the
overflow tank for coolant, many of today's vehicles make checking fluids a snap through
the use of semi-transparent plastic reservoirs in the engine compartment. By simply
looking at these containers, one can quickly see if they are low on brake fluid, power
steering fluid, or windshield washer fluid. Older vehicles used mostly metal reservoirs in
the engine compartment and these must be opened to check their level. Finally, a regular
battery inspection is also a good idea and can help avoid that dreadful feeling of turning
the ignition key and having nothing happen. Check the battery terminals and cables to see
that they are free of corrosion. Also check around the battery for signs or leakage. If
either of these conditions exists, you should have a mechanic look at it to see if the
battery is damaged or just needs to be cleaned up.
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Daily chassis inspection
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Check the engine, transmission, rear differential, power steering, and wheel seals
for lubricant or coolant leaks.
Check the condition of all belts, hoses, lines, (including such items as engine
belts, the fuel crossover lines, radiator hoses, water lines, air lines, power steering
lines, automatic transmission lines, etc).
Check the power steering for excessive play.
Check your air pressure and make sure your truck is building up air fast enough
and to the proper level.
Check tread and wear condition of all tires and check for too much or too little
pressure.
Check wheels and rims for any damage or cracks.
Check the brake shoes and drums for excessive wear or cracks.
Check your front axle and rear suspension for bad or cracked springs and or worn
bushing and pins.
Drain your air tanks daily. Check for excessive moisture.
Pay close attention to any frayed wiring and check battery connections.
Make sure all lights are operational.
Make sure your city and air horns are working.
Wipers must be working and always check your washer fluid.
Check your windshield and mirrors for visibility and cracks or chips.
Make sure you have a fire extinguisher and flares in the vehicle
Tire Pressures and Maintenance
Monitoring tire safety involves more than checking air pressure. Routine tire inspections
will help you identify problems with tires and other important systems.
Here's How:
1. Refer to the recommended tire pressure on sidewall of tire. You may also ask the
Shop Supervisor or mechanics for their recommendation.
2. Use a gauge to check the air pressure in each tire. Add air or deflate as needed to
match the manufacturer's recommendation. Use a remote style air chuck as to
remain away from danger in case of blowout.
Rule of Thumb: Pressure stats printed on sidewalls indicate the maximum amount of air
pressure tires should be inflated with -- not recommended pressures.
Drivelines
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Description and operation
A driveshaft is dynamically balanced to prevent excessive noise and vibration.
The driveshaft transmits torque from the transmission to the axle.
The driveshaft is composed of the universal joints, slip joints and connecting shafts.
The universal joints allow the driveshaft to operate with constantly charging angels
between transmission and axle.
The slip joint allows the length of the driveshaft to charge while transmitting torque.
Length charges are caused by necessary axle movement due to torque reaction, road
deflections, braking loads, etc.
The number of shaft and universal joints depends upon the vehicle wheelbase.
Center bearings are used for additional stability on extra long driveshaft.
All universal joints and sliding splines are equipped with grease fittings. Some center
bearing are equipped with grease fittings and others are pre-lubricated and sealed for the
life of the bearing. All universal joints and splines with grease fittings need to be kept in
grease so as not to be run dry. This prevents drive shaft failures caused by over heating.
Simply insert grease until the first visibly seen grease escapes the grease boot reservoir.
This will hold the lubrication needed to keep the union cool.
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Air Brakes
A "Compressed Air Brake System" is a different air brake used for trucks, consisting of a
standard disc or drum brake arrangement using compressed air in place of hydraulic fluid.
Most types of truck air brakes are drum units, though there is an increasing trend towards
the use of disc brakes in this application. The compressed air brakes system works by
drawing filtered air from the atmosphere, compressing it, and holding it in high-pressure
reservoirs at around 120 PSI. When needed for braking, this high pressure air is routed to
the operating cylinders on the brakes, which actuate the braking hardware and slow the
vehicle. Air brakes use compressed air to maximize braking forces.
Design and Function
A compressed air brake system is divided into a supply system and a control system. The
supply system compresses, stores and supplies high-pressure air to the control system as
well as to additional air operated auxiliary truck systems (gearbox shift control, clutch
pedal air assistance servo, etc.).
Supply system
"The air compressor is driven off of the engine either by crankshaft pulley via a belt or
directly off of the engine timing gears. It is lubricated and cooled by the engine
lubrication and cooling systems. Compressed air is first routed through a cooling coil and
into an air dryer the dryer device which removes moisture and oil impurities and also
may include a pressure regulator, safety valve and a smaller purge reservoir. As an
alternative to the air dryer, the supply system can be equipped with an anti freeze device
and oil separator. The compressed air is then stored in a reservoir (also called a wet tank)
from which it is then distributed via a four way protection valve into the front and rear
brake circuit air reservoir, a parking brake reservoir and an auxiliary air supply
distribution point. The system also includes various check, pressure limiting, drain and
safety valves.
Control System
The control system is further divided into two service brake circuits: the parking brake
circuit and the trailer brake circuit. This dual brake circuit is further split into front and
rear wheel circuits which receive compressed air from their individual reservoirs for
added safety in case of an air leak. The service brakes are applied by means of a brake
pedal air valve which regulates both circuits. The parking brake is the air operated spring
brake type where it’s applied by spring force in the spring brake cylinder and released by
compressed air via hand control valve. The trailer brake consists of a direct two line
system: the supply line (marked red) and the separate control or service line (marked
blue). The supply line receives air from the prime mover park brake air tank via a park
brake relay valve and the control line is regulated via the trailer brake relay valve. The
operating signals for the relay are provided by the prime mover brake pedal air valve,
trailer service brake hand control (subject to a country's relevant heavy vehicle
legislation) and the prime mover park brake hand control.
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Simplified brake diagram on a commercial vehicle
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1. air compressor,
2. pressure regulator,
3. air dryer,
4. regeneration reservoir,
5. four way protection valve,
6. compressed air reservoirs,
7. park brake hand control valve,
8. park brake safety release valve,
9. brake foot valve,
10. front air brake chambers,
11. brake relay valve + load sensing valve,
12. rear spring brake chambers,
Air Brake Components
Trailer brake relay valve
Park brake valve
Spring brake cylinderAir brake foot valve
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Truck air compressor
Air brake relay valve
Air dryer
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Rig-up
Tools
Plastic Buckets (Prohibited for Field Use)
Plastic buckets are not allowed for use as bleed off containment in the field. They have
been known to assist in the cause of static electricity fires and or explosions during
pressure bleed down and fluid draining applications.
Grounded Metal Buckets
Metal buckets with ground straps attached to a clean metal surface will assure a safe
release of controlled energy when bleeding off gas or fluids.
High Pressure Treatment Hoses
LRS employs the use of high pressure hoses to transfer fluids during treatment
procedures when applicable depending on job requirements. The flexibility of using a
hose allows for speedier rig-ups with fewer connections. Depending on job parameters,
LRS utilizes ½”, 1’, and 1½” hose with applicable hose pressure ratings.
Hose Chafe Protection
It is important to maintain the outer rubber layer of our High Pressure Treatment Hose.
After rigging up and before the pressure test, walk the line and check for any sharp edges
that might cause undo wear to the hose protective sheath. Place a nonabrasive shield
between the hose and suspect sharp edges using a rubber dog-dish or absorb as examples.
Hard-line
LRS employs high pressure tubing (hard-line) when higher pressures and pump rates are
required. Hard-line rig-ups are designed and set up to allow movement between the Unit
and treatment port using a minimum of 5 swivel points with no elevation change, or 7
swivel points with an elevation change. This is required so that pressure and pump
cavitation pulses do not put undo stress on rigging equipment. The Hard-line should be
off the ground and supported by stands at equal intervals in proximity to the hammer
unions (not under the hammer unions). Use plywood between the hard-line and spill
containment where the rig-up has to be on the ground. Spill containment needs to be
under all connections and Chiksan swivel joints.
Hammers
LRS hammers must be inspected before each use. They must be equipped with a non-slip
resistant friction tape with a ridge at the base of the handle to prevent the hammer from
escaping control from the user. No wooden or fiberglass handled hammers will be used in
the field.
Hand Tool Lanyards
LRS and our North Slope Clients are concerned with possible injuries and equipment
damage resulting from the loss of tool control. Lanyards are straps used to prevent tools
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from becoming dropped objects from one level to another below. We have an assortment
of different sizes and weight rated straps available to be used that will allow users
working at heights to maintain control of the tools being utilized.
Pipe Wrenches
Pipe wrenches used by LRS need to be inspected for defects before each use. The jaws
should be sharp as to maintain a grip on the object being turned. And the handle cannot
have a stress bend on it (usually caused by the use of a cheater bar or pipe). Any LRS tool
needs to be taken out of service if any structural or design flaws are found.
Chain Wrenches
LRS stocks all of the pump units with at least 1 chain wrench. Removal of tree-cap rings
and breaking free the tree-cap plugs is the main use. The chain wrench handle and chain
should be inspected for any flaws before each use. The use of a cheater bar or pipe will
usually compromise the integrity of the tool. Communicate with co-worker on difficult
tree-cap ring or plug extractions for assistance. Design a game plan for removal that will
maintain safety for those involved.
Jumper Lines
Jumper lines are used to allow the movement of fluid from one source to another while
keeping it in production to a process line, or to connect the tubing to the IA of the same
well to u-tube for a freeze protect. Pressure rated hard-line or hose are used depending on
rate required. The rig-up design must include shut in valves on both ends with shut-in
valve access port between to allow for pressure bleed off and to vacate fluid for the rigdown.
Bleed Hose
The common North Slope bleed hose is used to bleed pressure from tie in access ports to
bleed tanks. They are ½” high pressure rated hose usually in lengths 50’ or longer with
JIC female swivels on both ends.
The hose should be coiled up and connected snugly by a double male JIC fitting when
stored as to prevent a spill if any fluid remains after use.
Tree Cap Puller
Tree-cap pullers are used for removing difficult tree-cap plugs. There are two styles. One
works by tying into the ½” tree-cap gauge port with an all-thread bridge braced on the
flange ring below that connects the tree-cap bonnet, and lifting by thread rotation.The
other style is also threaded into the gauge port but is lifted by a lever action boom while
resting over a flange bolt connecting the tree-cap bonnet.
“Line of Fire”
Line of Fire is a term meaning “in possible harms way” if something goes wrong. It is
imperative that one respects the danger of an uncontrolled release of energy. This may
mean anywhere from standing under a suspended load to standing in front of a closed
valve (without a positive block plug) that has pressure behind it. A suspended load may
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shift, a closed valve may fail. Never take a chance by believing any mechanical device is
fail safe. This also applies to human error.
Pre-job Inspection
A Pre-job walk-around should be performed by the crew before initiating the Pre-job
checklist. The intent is to identify existing concerns that might affect the safe
performance of the job scope, and also to list any pre-existing concerns that were left
from prior activities.
Walk-around
A Walk around is LRSI slang for visually checking all of the components involved on a
job site that LRS has control of. This means looking for drips and leaks under or around
the equipment, and tie-ins (well head, manifold building, facility, etc). Checking for tire
damage, rims, lugs, under carriage suspension components, pump drive lines, opening
access doors in the pump room or gen shed looking for leaks or mechanical issues,
checking the temperatures and pressures in the tractor cabs, repetitive checks on the
pressures on the wellhead (I.A, O.A., tubing, flow-line, hydraulic pressures on the ESD
panels, etc..), bleed tank levels, tank or transport connections and levels, checking on
wind direction, other people not authorized to be in the area, etc..
The person performing the walk-around needs to communicate with the operator that
everything is good, or if there is a problem, to inform the operator on what issues exist
that needs attention.
A Walk-around should be done every 10 minutes during pumping operations, and 15
minutes, depending on job status, during stand-by.
Post Job Inspection
A Post Job inspection is required after performing the Rig-down of a job procedure to
insure the worksite is clean of any contaminates, and that all tools and materials have
been retrieved and placed in the appropriate storage areas.
The Operator is responsible to ensure all valves and surface equipment is returned to their
respective correct positions. And to communicate any issues pertaining to the job with the
Job Site Authority (Pad Operator, Plant Operator, etc.).
H2S Personal Monitor
This is a personal safety device that warns when hazardous gas exceeds factory set alarm
set-points (10 ppm). It is your responsibility to respond properly to the alarms.
Periodically test the response of the sensor to gas by exposing the detector to a target gas
concentration that exceeds the low alarm set-point. Manually verify that the audible and
visual alarms are activated.
Ports
(Tie–Ins)
A port is a term LRS uses to signify a type of valve to rig up to that can be used for
access on pumping operations. A good port or tie-in allows you to isolate and bleed
pressure off for a safe rig-up and rig down.
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Needle Valves
A needle valve is a type of valve having a small orifice and a threaded, needle-like
plunger. It allows precise regulation of flow, although it is generally used for, and is
capable of, only relatively small flow rates. A needle valve has a relatively small orifice
with a long, tapered, conical seat. A needle-shaped plunger, on the end of a screw,
exactly fits this seat. As the screw is turned and the plunger retracted, flow between the
seat and the plunger is possible; however, until the plunger is completely retracted the
fluid flow is significantly impeded. Since it takes many turns of the fine-threaded screw
to retract the plunger, precise regulation of the flow rate is possible. Needle valves are
usually used in flow metering applications, especially when a constant, calibrated, low
flow rate must be maintained for some time, such as the idle fuel flow in a carburetor.
Since flow rates are low and many turns of the valve stem are required to completely
open or close, needle valves are not used for simple shutoff applications.
Since the orifice is small and the force advantage of the fine-threaded stem is high, needle
valves are usually easy to shut off completely, with merely "finger tight" pressure. Small,
simple needle valves are often used as bleed valves.
Unlike a ball valve, or valves with a rising stem, it is not easy to tell from examining the
handle position whether the valve is open or closed.
It is not an acceptable practice to rig up to needle valves except with a bleed hose to gain
access. Trace down the plumbing with a company Rep to find a better access port to tie
into. Only in extreme instances with the consent of your LRSI Operations Field
Supervisor is this allowed. Pumping through a needle valve creates an unacceptable
pressure differential. It also has a high potential to wash out the stem seal which would
make it difficult to rig down from.
Ball Valves
A ball valve is a valve that opens by turning a handle attached to a ball inside the valve.
The ball has a hole, or port, through the middle so that when the port is in line with both
ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to
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the ends of the valve, and flow is blocked. The handle or lever will be inline with the port
position letting you "see" the valve's position. The ball valve, along with the butterfly
valve and plug valve, are part of the family of quarter turn valves.
Ball valves are durable and usually work to achieve perfect shutoff even after years of
disuse. They are therefore an excellent choice for shutoff applications (and are often
preferred to globe valves and gate valves for this purpose). They do not offer the fine
control that may be necessary in throttling applications but are sometimes used for this
purpose.
Ball valves are used extensively in industry because they are very versatile, pressures up
to 10,000 psi, temperatures up to 200 Deg C. Sizes from 1/4" to 12" are readily available
They are easy to repair, operate manually or by actuators.
The body of ball valves may be made of metal, plastic or metal with a ceramic center.
The ball is often chrome plated to make it more durable.
Gate Valves
A gate valve, also known as a sluice valve, is a valve that opens by lifting a round
gate/wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing
surfaces between the gate and seats are planar. The gate faces can form a wedge shape or
they can be parallel. Typical gate valves should never be used for regulating flow, unless
they are specifically designed for that purpose. On opening the gate valve, the flow path
is enlarged in a highly nonlinear manner with respect to percent of opening. This means
that flow rate does not change evenly with stem travel. Also, a partially open gate disk
tends to vibrate from the fluid flow. Most of the flow change occurs near shutoff with a
relatively high fluid velocity causing disk and seat wear and eventual leakage if used to
regulate flow. Typical gate valves are designed to be fully opened or closed. When fully
open, the typical gate valve has no obstruction in the flow path, resulting in very low
friction loss.
Gate valves are characterized as having either a rising or a nonrising stem. Rising stems
provide a visual indication of valve position. Nonrising stems are used where vertical
space is limited or underground.
Bonnets provide leak proof closure for the valve body. Gate valves may have a screw-in,
union, or bolted bonnet. Screw-in bonnet is the simplest, offering a durable, pressuretight seal. Union bonnet is suitable for applications requiring frequent inspection and
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cleaning. It also gives the body added strength. Bolted bonnet is used for larger valves
and higher pressure applications.
Another type of bonnet construction in a gate valve is pressure seal bonnet. This
construction is adopted for valves for high pressure service, typically in excess of 2250
psi. The unique feature about the pressure seal bonnet is that the body - bonnet joints
seals improves as the internal pressure in the valve increases, compared to other
constructions where the increase in internal pressure tends to create leaks in the bodybonnet joint.
Check Valve
This is a mechanical device that permits fluid to flow or pressure to act in one direction
only. Check valves are used in a variety of oil and gas industry applications as control or
safety devices. Check valve designs are tailored to specific fluid types and operating
conditions. Some designs are less tolerant of debris, while others may obstruct the bore of
the conduit or tubing in which the check valve is fitted.
The check valve should be positioned as close to the well or tie-in point as possible to
provide the highest level of protection possible in the event of a hose or containment
failure during operation by limiting the amount of line that is behind the checkvalve.
All LRS check valves are considered critical to safe operations and as such are on the
Safety Critical Equipment List.
Low Torque High Pressure ¼ Turn (Weco Plug Valve)
Weco plug valves are quarter-turn valves designed for a wide range of standard and sour
gas drilling, production and well-servicing applications. These valves come in single and
dual-body designs in pressures to 20,000psi. They range in size from two to four inches
and come with 1502 threaded and wing unions. They are designed with a two piece
floating Plug / Stem, and are capable of handling fluids with solids intermixed. This plug
valve is used throughout the field in temporary set-ups such as flow-backs, Coiled
Tubing, Well Testing, Fracs, etc..
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Types of Jobs
Assists
Coil Tubing
Coiled tubing (CT) has been used at Prudhoe Bay since the early 1980's, for such
operations as cement squeezing, well cleanouts, stimulation, inflatable packers and plug
placements, fishing, and temporary artificial lift applications previously performed by
drilling/work-over rigs. The majority of these CT jobs are conducted with 1-3/4" OD CT
which has proven to have excellent strength, capacity, and durability for typical field
operations. With the recent availability of 2.0", 2-3/8", 2-7/8" and 3-1/2" OD CT,
additional drilling and production applications once thought improbable to impossible
have been achieved.
As in many oil fields of the world, CT is commonly used for cleanouts, stimulations, well
kick-offs (N2 or jet pump), and spotting of various fluids. In addition to these
applications, coiled tubing is routinely used for cement squeeze work, running inflatable
packers and bridge plugs, milling and under-reaming hard fill or cement, pressure
isolation inside existing tubing (patches), running electric line logs in highly deviated
wells, and fishing operations. Relatively new CT applications, including re-completions,
tubing or casing cutting operations, and drilling - are becoming more commonplace.
 Ice Plug Jetting - LRS assists Coil Tubing during ice plug jetting to heat and
pump fluid (usually diesel) on wells that are restricted by ice or hydrate plugs.
The tie-in port for the hot oil unit is located usually at the high pressure manifold
at the reel.
 Coil Stuck in Hole - Coil Tubing sometimes get stuck down hole for various
reasons. LRS may be summoned to assist by rigging up to the CT lubricator tie in
point (or elsewhere, depending on situation) and pump fluid down hole to flush
material (sand, scale, etc) away from the coil tubing, that may be hanging them
up.
Wireline (E-line)
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In the oil and gas industry, the term wireline usually refers to a cabling technology used
by operators of oil and gas wells to lower equipment or measurement devices into the
well for the purposes of well intervention and reservoir evaluation.
Braided line can contain an inner core of insulated wires which provide power to
equipment located at the end of the cable, normally referred to as electric line, and
provides a pathway for electrical telemetry for communication between the surface and
equipment at the end of the cable.
 Bridge Plug Pressure Test - A down-hole tool that is located and set to
isolate the lower part of the well-bore. Bridge plugs may be permanent or
retrievable, enabling the lower well-bore to be permanently sealed from
production or temporarily isolated from a treatment conducted on an upper
zone. LRS will tie in to the E-line lubricator and pressure up against the plug
to ensure it holds pressure.
 Camera - A live feed camera with the ability to record is run down hole to
diagnose problems in a wide variety of applications. LRS is used to pump
filtered fluid down hole to flush away and clean up the viewing area as to give
the camera the ability to have a clear picture to decipher well issues.
 Leak Detect - There are several ways that LRS can assist E-line in leak
detection depending on the severity of a suspected leak and the type of tool
that E-line may use. Pumping fluid down the IA (inner annulus) while E-line
lowers their Temperature or Noise Log tool in the tubing are options.
 Stuck Tool String - E-line may have an issue running in or out of the well by
hanging up and getting stuck. LRS may be dispatched to rig up and pump
fluid to free their tool-string.
 Pump-down Assist - A vast majority of wells are drilled at an angle to
support production from the surrounding area of a drill-site. The angle of drop
might necessitate the use of a pump to assist E-line to the depth needed for
their procedure.
 Lubricator Pressure Test - It is standard procedure on the North Slope for
contractors connected to wellheads for well work to pressure test their surface
equipment before opening up.
Frac (Fracturing)
Often an oil- or gas-bearing formation may contain large quantities of oil or gas, but have
a poor flow rate due to low permeability, or from damage or clogging of the formation
during drilling. This is particularly true for tight sands, oil shales and coalbed methane.
Hydraulic fracturing (also known as fracking) is a technique used to create fractures that
extend from the well bore into rock or coal formations. These fractures allow the oil or
gas to travel more easily from the rock pores, where the oil or gas is trapped, to the
production well. Typically, in order to create fractures a mixture of water, proppants
(sand or ceramic beads) and chemicals is pumped into the rock or coal formation at fast
rates and high pressures.
Eventually, the formation will not be able to absorb the fluid as quickly as it is being
injected. At this point, the pressure created causes the formation to crack or fracture. The
fractures are held open by the proppants, and the oil or gas is then able to flow through
the fractures to the well.
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Fluid Heating - Due to the use of a gelling agent mixed on the fly with fluid
(usually sea water) in an arctic environment and pumping this mixture with
propant through up to 2000’ of permafrost. It is imperative that the fluid be
warm. LRS will be called in to circulate and heat 500bbl capacity frac tanks
(up to 11,000bbls of fluid).
IA Pressure Control - Pumping the frac down at a high rate and high
pressure (up to 45bpm at10000psi) puts undo force on the tubing. It is
imperative to maintain a constant elevated pressure on the fluid packed inner
annulus (usually 3500psi). Usually the job setup includes a Pressure Relief
Skid that is set for the maximum IA pressure allowed. This setup is hardlined
a safe distance away and connects to a tank for the fluid that releases should
the frac plug off during the procedure. LRS monitors the IA pressure and
pressures up or bleeds off to maintain the constant IA pressure prescribed.
Line Flush / Tree Saver Retrieval - If the frac procedure plugs off. There is
the possibility that LRS will be asked to assist in freeing up the Tree Saver.
This entails rigging off the Pressure Relief Skid and moving to the Tree Saver
rig up assembly and flushing the line to a bypass open top tank.
Slickline
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Slickline is a long, smooth, unbraided wire that is chrome in appearance. It comes in
varying lengths, according to the depth of wells in the area it is used (it can be ordered to
specification) up to 35,000 feet in length. It is used to lower and raise downhole tools
used in oil and gas well maintenance to the appropriate depth of the drilled well. In use
and appearance it is connected by the drum it is spooled off of in the back of the slickline
unit to the wireline sheave (a round wheel grooved and sized to accept a specified line
and positioned to redirect the line to another sheave that will allow it to enter the device
that allows the slickline to enter the wellbore while keeping the pressure contained and
wiping the messy and sometimes hostile downhole fluids from the line. Slickline is used
to lower downhole tools into an oil or gas well to perform a specified maintenance job
downhole. Downhole refers to the area in the pipe below surface, the pipe being either
the casing cemented in the hole by the drilling rig (which keeps the drilled hole from
caving in and pressure from the various oil or gas zones downhole from feeding into one
another) or the tubing, a smaller diameter pipe hung inside the casing that is the conduit
for (oil, water or gas) the well to flow through.
Uses
Slickline is more commonly used in production tubing. The wireline operator monitors at
surface the slickline tension via a weight indicator gauge and the depth via a depth
counter 'zeroed' from surface, lowers the downhole tool to the proper depth, completes
the job by manipulating the downhole tool mechanically, checks to make sure it worked
if possible, and pulls the tool back out by winding the slickline back onto the drum it was
spooled from. The slickline drum is controlled by a hydraulic pump, which in turn is
controlled by the “slickline operator”.
Slickline comes in different sizes and grades. The larger the size, and higher the grade,
generally means the higher line tension can be pulled before the line snaps at the weakest
spot and causes a costly 'fishing' job. Due to downhole tools getting stuck because of
malfunctions or 'downhole conditions' including sand, scale, salt, asphaltenes, and other
well byproducts settling or loosening off the pipe walls because of agitation either by the
downhole tools or a change in downhole inflow, sometimes it is necessary to pull hard on
the tools to bring them back uphole to surface. If the tools are stuck, and the operator
pulls too hard, the line will snap or pull apart at the weakest spot, which is generally
closer to surface as the further uphole the weak point in the line is, the more weight it has
to support (the weight of the line).
Weak spots in the line can be caused by making the circle around the counter wheel,
making a bend around a sheave, a kink in a line from normal use (when rigging up the
equipment extra line must be pulled out from the truck to give enough slack when the
pressure control lubricator is picked up - this leaves line coiled on the often rutted
ground, and sometimes it snags and kinks the line).
When the slickline parts. It can create an expensive 'fishing' job. It is called fishing
because you often have to try different 'fishing' tools until you get a 'bite', then you have
to work the original tools downhole free, or cut off the slickline where they join the tools
downhole so that you can pull the broken slickline back to surface and out of the way, in
order to fish the stuck toolstring. Because of the downtime involved in 'fishing', meaning
not being able to flow the oil/gas well, the client is losing money by lack of production
and also the cost of the slickline unit to fish, and the cost of what is left in the hole if it is
not fished out (in the oil/gas industry, if the cause of the fishing job was not the fault of
the slickline company, the oil/gas company is usually responsible to pay for it, and it can
be very expensive).
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Slickline was originally called measuring line, because the line was flat like a tape
measure, and marked with depth increments so the operators would know how deep in
the hole they were. This probably changed because the flat measuring line wasn't as
strong as the modern slickline, and separate depth counters were developed. It is
advantageous to keep the diameter of the wire as small as possible for the following
reasons:
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It reduces the load of its own weight.
It can be run over smaller diameter sheaves, and wound on smaller diameter
spools or reels without overstressing by bending (where the wire bends makes it
weaker. Where it makes a complete circle, such as a counter wheel, makes it
weaker yet).
It keeps the reel drum size to a minimum (which reduces the area needed in the
back of the slickline unit to house the drum and hydraulic pump, reducing weight
and leaving more room for the other specialized equipment needed for slickline
operations).
It provides a small cross-section area for operation under pressure.
The disadvantage of a smaller diameter slicklne is the lower strength. Depth and the
nature of the job (a tool that must be pulled hard or might be stuck) will affect what
slickline truck (different trucks specialize in different sizes of line) used.
The sizes of solid wireline in most common uses are: 0.092", 0.108", 0.125", 0.140",
0.150", and 0.160" in diameter, and are obtainable from the wire-drawing mills in onepiece standard lengths of 18,000, 20,000, 25,000 and 30,000 foot lengths. Other
diameters and lengths are usually available on request from the suppliers, with the largest
size currently available at 0.188".
Lubricator – The long assembly of pressure rated pipe installed on top of the wellhead
that houses the toolstring that is run in and out of the hole. The lubricator should be long
enough to be able to swallow the toolstring and downhole tools that are to be run or
pulled.
Applications - The most common applications for slickline are:
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Tagging a T.D (tubing depth). The furthest depth possible down the wellbore.
Gauge Ring runs - Running a special sized downhole tool called a gauge ring,
which comes in various pre-machined diameters, designed to ensure the pipe is
clear to a certain point.
Broach tubing / Plunger Installations - A tubing broach looks like an aggressive,
tubular file, available in different diameters, used for removing burrs and crimps
in the inside of tubing and casing in oil and gas wells.
Bailing sand and debris - Removing formation sand/rock and other such debris
left over from the drilling and completion of the well, using a specialized tool
called a bailer. This tool uses either a Chinese water pump type stroke action or a
hydrostatic vacuum action to suction up the downhole debris, allowing it to be
conveyed back to surface via the wireline.
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Shifting sleeves - Formations downhole can be isolated behind sliding metal
'windows' called sliding sleeves. They are shifted open or closed by means of a
specialized shifting tool locating the sleeve and it being jarred up or down,
providing access or closing off that formation or section of casing.
Setting and Pulling, plugs and chokes - Specialized downhole tools which either
lock into pre-machined restrictions in the tubing, or which lock into the tubing
itself, sealing pressure from below or above the plug.
Setting and Pulling, gas lift valves - Adjustable regulated valves that are housed
in mandrels that allow gas to flow at a designed pressure from the inner annulus
into the tubing that mixes with and lightens the producing oil that brings it to the
surface.
Bottomhole pressure and temperature surveys - Specialized electronic and
mechanical tools designed to measure the pressure and temperature at
predetermined depths in the wellbore. This data can be used to determine
reservoir life.
Spinner Surveys - To determine which formation perforations have the best
inflow / which perforations make the most water / liquids.
Kinley perforator, sandline cutter, and caliper.
Running production logging tools.
Fishing operations - Fishing usually refers to attempting to retrieve lost tools or
wire, or other debris that was not intended to restrict the flow / disrupt the well
operations. Fishing can be difficult, due the fish being downhole, and other
affecting conditions such as high pressure, the fish being jammed in the tubing /
casing.
Paraffin cutting - Making a hole through and removing a wax buildup, which is a
byproduct of oil cooling too much before it reaches surface.
Chipping ice - Restrictions and plugs which can be formed as by products of a
flowing well.
A sample of LRS assisted Slickline Job Tasks:
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Jet Pump
Leak Detect
Over Displace (Pulling a Plug or Valve)
Pressure Test
Pump-down Assist
Set Valve
Tubing Displacement
Tubing Flush
SSSV (Brush and Flush)
Paraffin Cut
Ice Plug
Freeze Protect
ESP (Electrical Submergible Pump)
MIT (mechanical integrity test)
Pre and post frac
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Biocide Pumping (Corrosion Related)
Biocide pump jobs are necessary to prevent bacterial growth and the production of
biogenic (bacterially generated) hydrogen sulfide in production process equipment and
reduce corrosion. The three main ingredients that compose Biocide are ethanol,
Glutaraldehyde, and Ethylene Glycol.
Precautions including special training and PPE are needed when handling this chemical.
Chemical Squeeze (Corrosion Related)
The squeeze procedure consists of the following basic steps:
 Mutual solvent pre-flush: prevent possible sludge formation
 Demulsifier: prevent possible emulsion generated, spacer of fresh water
 Surfactant: clean the tubing and well bore formation to prevent oily deposits from
pushing into formation and affect the squeeze performance on rock matrix
 Scale inhibitor: the main treatment, over flush with fresh water
 Displacements: Seawater or produced water to assist unloading the well after shut
in period
 Shut in time for better adsorption /desertion profile
After squeeze job and during well start up, representative samples are collected to
determine effectiveness.
Circ Out
A general term used to reference a procedure in which a tubing plug is set with a side
pocket to the Inner Annulus left open. Fluid is then pumped down-hole in either direction
and returned to surface making it possible to fluid pack both tubing and IA with specific
fluids. This procedure can be used to recover costly fluids used for weight purposes by
taking returns into surface tanks to be reconstituted and used again.
Displacement
A displacement is simply pumping a preferred fluid down-hole to displace well-bore
fluids for many possible reasons usually regarding down-hole service work.
Drilling Rig
LRS assists drilling rigs mainly in two procedures, wellbore freeze protection, and
heating fluids for constructing mud used in circulation in the drilling process.
Flowline Pressure Test
A pressure test on a flowline is required for all new construction surface lines and
anytime an existing line is reattached.
Fluid Heating
LRS heats many different types of fluid in varying vessels for oilfield production or
drilling.
Fluid Transport
LRS may be called on to load a fluid to be delivered to a location.
Flushes
A wellbore may need to be cleaned up for a number of reasons depending on the
procedure. This usually entails the use of diesel.
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Flushes are performed to clean up surface lines for repairs or line replacement, and for
vessel inspections.
Note: A flush on surface lines and vessels usually entails the use of diesel as a solvent
followed by a rinse using soapy water.
Freeze Protect
Due to arctic temperatures, freeze protections may be warranted for all surface equipment
that may have any water content that is not moving. Well freeze protections are year
round due to the permafrost that may run as low as 2000 feet below surface.
High Pressure Break Down
A High Pressure Breakdown is performed on a water injection well to improve injection
rate.
Hot Diesel Flush
This procedure is nothing more than pumping hot diesel down the tubing for varying
reasons as in warming up and cleaning the tubing when bringing a well back on line to
production.
Ice Plug Thaw
Arctic temperatures and a permafrost layer of up to 2000 feet below surface may create
an ice plug anywhere water may lie dormant. LRS may use a number of ways to thaw
these plugs depending on variables regarding each case.
 Tubing
 Annuli
 Flow-lines
 Vessels
 Ground Thaws
Injectivity Test
An Injectivity test is nothing more than just pumping a fluid and establishing a rate and
pressure that may be required information for well design or formation data.
MIT (Mechanical Integrity Test)
Mechanical Integrity Tests (MIT) on producing, disposal, and enhanced oil recovery
(injection) wells are required by both state and federal regulatory authorities. Both
authorities are seeking assurance that well bore fluids cannot migrate to strata from which
the well is intended to be isolated. This is accomplished by subjecting the well bore, any
annuli and isolation hardware such as packers to pressures at or above the maximum
design pressure.
Pig Launching
Pigging in the context of pipelines refers to the practice of using pipeline inspection
gauges or 'pigs' to perform various maintenance operations on a pipeline.
These operations include but are not limited to cleaning and inspecting of the pipeline.
This is accomplished by inserting the pig into a “pig launcher” (or launching station) - a
funnel shaped Y section in the pipeline. The launcher / launching station is then closed
and the pressure driven flow of the product in the pipeline is used to push it along down
the pipe until it reaches the receiving trap - the 'pig catcher' (or receiving station).
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LRS may be asked to assist in the launching of pigs by pumping fluid and increasing the
rate to get the pig out of the launcher and into the pipe.
Pipeline Pumping
There are many different scenarios in which LRS may be called to pump fluids into
pipelines.
Pressure Tests - Surface Equipment
 Facility
 Flowline
 Hardline
 Lubricators
 Manifold Building
 Vessel
 Well Testing Rig-up
Science Project
A term used to describe an untried or new procedure.
Steam Job
Steam jobs are usually associated with cleaning equipment or facilities that may benefit
in appearance from indoor spills to normal year to year facility usage. The work will
usually utilize ½ “steam hose connected with JIC fittings with a steam wand at the end
for spraying hot water under pressure.
Another application of using hot water with pressure is the ability of thawing ice plugs in
culverts using a “Wiggle Wart” tool that is self propelled by using jets that push if
forward.
 Culvert
 Facility Spill
 Ground Thaw
 Vessel
 Wellhouse
Tank Heating
WAG Wells (Water Alternating Gas Injection)
The WAG injection is a process that enables the ability to produce more oil out of oil
bearing reservoirs. Water injection alone tends to sweep the lower parts of a reservoir,
while gas injected alone sweeps more of the upper parts of a reservoir owing to
gravitational forces. The ability to swap these two processes aids the reservoir engineers
in oil reservoir control.
 Water to Gas – LRS will load and pump a methanol pill to keep the well from
freezing up.
 Gas to Water – LRS will load and pump a prescribed fluid that will
overbalance
the higher gas pressure and allow water to be injected at a
lower pressure.
Well Kill
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Is how to stop a well from flowing or having the ability to flow into the well-bore. Kill
procedures typically involve circulating reservoir fluids out of the wellbore or pumping
higher density mud into the wellbore, or both. In the case of an induced kick, where the
mud density is sufficient to kill the well but the reservoir has flowed as a result of pipe
movement, the driller must circulate the influx out of the wellbore. In the case of an
under-balanced kick, the driller must circulate the influx out and increase the density of
the drilling fluid. In the case of a producing well, a kill fluid with sufficient density to
overcome production of formation fluid is pumped into the well to stop the flow of
reservoir fluids.
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Well Head (Tree)
A wellhead is a general term used to describe the component that is used to suspend
casing strings and provide sealing functionality for oil wells. Wellheads can be
located on oil platforms, subsea or onshore. A wellhead system provides the
following basic functions
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Provide a means of casing suspension. (Casing is the permanently installed
pipe used to line the well hole for pressure containment and collapse
prevention during the drilling phase)
Provides a means of tubing suspension. (Tubing is removable pipe installed in
the well through which well fluids pass)
Provides a means of pressure sealing and isolation between casing at surface
when many casing strings are used
Provides pressure monitoring and pumping access to annuli between the
different casing/tubing strings
Provides a means of attaching a blowout preventer during drilling
Provides a means of attaching a Christmas tree for production operations
Provides a reliable means of well access
Provides a means of attaching a well pump
Components - The primary components of a wellhead system are:
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Casing spool – holds the outermost casing and the innermost casing is hung
from casing slips
Tubing spool – holds the production casing and production tubing
casing slips - what the production casing hangs from in side the casing spool
Pack-offs and isolation seals – isolate production casing and the tubing spool
profile
Test plugs (back pressure valve/2 way check) used in drilling and well
securing operations
Tubing head adaptor/seal flange – isolates the top outer profile of the tubing
hanger to tree
Specification - The basic requirements for materials, dimensions, test procedures and
pressure ratings for wellheads and wellhead equipment are defined within API Spec 6A:
Specification for Wellhead and Christmas Tree Equipment. Wellheads are cemented in
place and are generally permanently kept in place, although in exploration wells they may
be recovered for use again. Copies of API 6A are available from the Field Supervisor.
Design factors - Wellheads are manufactured in a vast variety of manners for numerous
purposes which dictate design. Factors that affect wellhead configuration are pressure,
temperature, location, well depth, well size, well purpose, expected well life, well control
equipment interface, drilling method, etc.
Functions - A wellhead serves numerous functions. Some of these are:
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Means of casing suspension. (Casing is the permanently installed pipe used to line
the well hole for pressure containment, collapse prevention, etc.)
Means of casing pressure isolation when multiple casing strings are used
Means of attaching a blowout preventer during drilling
Means of attaching a tree for well control during production, injection, or other
operations
Means of well access
Means of pump attachment
Means of tubing suspension (Tubing is removable pipe installed in the well)
Listed in Order from Top to Bottom
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Swab Valve
The topmost valve on a Christmas tree that provides vertical access to the wellbore
Wing Valve
A valve located on the side of a Christmas tree or temporary surface flow equipment,
such as may be used for a drill-stem test. Two wing valves are generally fitted to a
Christmas tree. A flowing wing valve is used to control and isolate production, and the
kill wing valve fitted on the opposite side of the Christmas tree is available for treatment
or well-control purposes. The term wing valve typically is used when referring to the
flowing wing.
Companion Valve
A valve usually on the opposite side of the Wing Valve used for accessing the well for
down-hole stimulations without subjecting the production side of the well with higher
pressures or fluids not meant for flow lines.
Surface Safety Valve (SSV)
Surface safety valve (SSV) is a hydraulically actuated fail-safe gate valve for producing
or testing oil and gas wells with high flow rates, high pressures, or the presence of H2S.
The SSV is used to quickly shut down the well upstream in the event of overpressure,
failure, a leak in downstream equipment, or any other well emergency requiring an
immediate shut down.
A SSV is remotely operated by an emergency shutdown device (ESD), which can be
triggered automatically by high or low pressure pilot actuators. If an emergency occurs,
this feature reduces the possibility of personnel injuries.
Master Valve
A valve located on the side of a Christmas tree or temporary surface flow equipment,
such as may be used for a drill-stem test. Two wing valves are generally fitted to a
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Christmas tree. A flowing wing valve is used to control and isolate production, and the
kill wing valve fitted on the opposite side of the Christmas tree is available for treatment
or well-control purposes. The term wing valve typically is used when referring to the
flowing wing.
Sub Surface Safety Valve (SSSV)
Sub surface safety valve (SSSV) is a hydraulically actuated fail-safe ball or flapper-style
valve used in producing or testing oil and gas wells with high flow rates, high pressures,
or the presence of H2S. The SSSV is used to quickly shut down the well upstream in the
event of overpressure, failure, a leak in downstream equipment, or any other well
emergency requiring an immediate shut down. The valve may be either surface controlled
or subsurface controlled.
Lateral or Pit Valve
A valve located downstream of the wing valve on the production or flow line that can be
used as a block valve between the well and production facility (Manifold Building).
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Facilities
Choke
A choke is a control device with an orifice that is used to regulate a fluid or gas flow rate,
or downstream system pressure. Chokes are available in several configurations for both
fixed and adjustable modes of operation. Adjustable chokes enable the fluid or gas flow
and pressure parameters to be changed to suit process or production requirements. Fixed
chokes do not provide this flexibility, although they are more resistant to erosion under
prolonged operation or production of abrasive fluids.
Separator
A cylindrical or spherical vessel used to separate oil, gas and water from the total fluid
stream produced by a well. Separators can be either horizontal or vertical.
Separators can be classified into two-phase and three-phase separators (commonly called
free-water knockout). The two-phase type deals only with oil and gas, while the threephase type handles oil, water and gas. Additionally, separators can be categorized
according to their operating pressure. Low-pressure units handle pressures of 10 to 180
psi. Medium-pressure separators operate from 230 to 700 psi. High-pressure units handle
pressures of 975 to 1500 psi.
Gravity segregation is the main force that accomplishes the separation, which means the
heaviest fluid settles to the bottom and the lightest fluid rises to the top. Additionally,
inside the vessel, the degree of separation between gas and liquid will depend on the
separator operating pressure, the residence time of the fluid mixture and the type of flow
of the fluid. Turbulent flow allows more bubbles to escape than laminar flow.
Vapor Recovery Unit
A system composed of a scrubber, a compressor and a switch. Its main purpose is to
recover vapors formed inside completely sealed crude oil or condensate tanks.
The switch detects pressure variations inside the tanks and turns the compressor on and
off. The vapors are sucked through a scrubber, where the liquid trapped is returned to the
liquid pipeline system or to the tanks, and the vapor recovered is pumped into gas lines.
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Conventional separators and fluid measurements: Production separation begins with well
flow-streams entering a vessel horizontally and hitting a series of perpendicular plates.
This causes liquids to drop to the bottom of the vessel while gas (red) rises to the top.
Gravity separates the liquids into oil (brown) and water (blue). The gas, oil and water
phases are metered individually as they exit the unit through separate outflow lines.
Mechanical meters measure fluids; an orifice meter measures the gas. Both devices
require periodic recalibration.
Test Separator
A vessel used to separate and meter relatively small quantities of oil and gas. Test
separators can be two-phase or three-phase, or horizontal, vertical or spherical. They can
also be permanent or portable.
Test separators sometimes are equipped with different meters to determine oil, water and
gas rates, which are important to diagnose well problems, evaluate production
performance of individual wells and manage reserves properly.
Test separators can also be called well testers or a well checkers.
Two-phase Separator
Is a vessel that separates the well fluids into gas and fluid. A two-phase separator can be
horizontal, vertical or spherical. The liquid (oil, emulsion) leaves the vessel at the bottom
through a level-control or dump valve. The gas leaves the vessel at the top, passing
through a mist extractor to remove the small liquid droplets in the gas.
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Down-hole Information
Well Types
 Production Wells
 Injection Wells
o Sea Water Injection
o Produced Water Injection
o Gas Injection (Dry)
o M.I. Injection (Wet)
 Disposal Wells
Wellhead and Down Hole Gas Lift Oil Producer Configuration
An artificial-lift method in which gas is injected into the production tubing to reduce the
hydrostatic pressure of the column of fluid. The resulting reduction in bottom-hole
pressure allows the reservoir liquids to enter the wellbore at a higher flow rate. The
injection gas is typically conveyed down the tubing-casing annulus and enters the
production train through a series of gas-lift valves. The gas-lift valve position, operating
pressures and gas injection rate are determined by specific well conditions.
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Annulus
The space between two concentric objects, such as between the wellbore and casing or
between casing and tubing, where fluid can flow. Pipe may consist of drill collars, drillpipe, casing or tubing.
Injection Well
A well in which fluids are injected rather than produced. The primary objective typically
being to maintain reservoir pressure. Two main types of injection are common: gas and
water. Separated gas from production wells or possibly imported gas may be re-injected
into the upper gas section of the reservoir. Water-injection wells are common offshore,
where filtered and treated seawater is injected into a lower water-bearing section of the
reservoir.
Disposal Well
A well (often a depleted oil or gas well), into which waste fluids can be injected for safe
disposal. Disposal wells typically are subject to regulatory requirements to avoid the
contamination of freshwater aquifers.
Thermal Expansion
Thermal Expansion is the tendency of matter to change in volume in response to a change
in temperature. When a substance is heated, its constituent particles move around more
vigorously and by doing so generally maintain a greater average separation. Materials
that contract with an increase in temperature are very uncommon; this effect is limited in
size, and only occurs within limited temperature ranges. The degree of expansion divided
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by the change in temperature is called the material's coefficient of thermal expansion and
generally varies with temperature.
Permafrost exists on the North Slope. This is a geological layer that is permanently
frozen down to 1800 feet from the surface. When we pump hot fluids down hole or bring
a shut-in well back on line. A heat exchange will occur. A constant watch on pressures
during well procedures is vital so as not to over pressure and damage the inner or outer
annulus.
Down-Hole Components and Tools
Accumulator
A device used in SSV (Surface Safety Valve) and SSSV (Sub Surface Safety Valve)
hydraulic systems to store energy, or in some applications, dampen pressure fluctuations.
Energy is stored by compressing a pre-charged gas bladder with hydraulic fluid from the
operating or charging system. Depending on the fluid volume and pre-charge pressure of
the accumulator, a limited amount of hydraulic energy is then available independent of
any other power source. Well pressure-control systems typically incorporate sufficient
accumulator capacity to enable the blowout preventer to be operated with all other power
shut down.
Back Pressure Valve
A type of check valve, typically installed in the tubing hanger, to isolate the production
tubing. The back-pressure valve is designed to hold pressure from below yet enable fluids
to be pumped from above, as may be required for well-control purposes.
Bridge Plug
A down-hole tool that is located and set to isolate the lower part of the wellbore. Bridge
plugs may be permanent or retrievable, enabling the lower wellbore to be permanently
sealed from production or temporarily isolated from a treatment conducted on an upper
zone.
Broach
A down-hole tool used to repair the internal diameter of the production tubing where a
slight collapse or a dent has occurred. Cutting profiles on a broach removes the tubingwall material to allow subsequent passage of tools and equipment of a prescribed
diameter.
Caliper Log
Is a procedure that shows a representation of the measured diameter of a borehole along
its depth. Caliper logs are usually measured mechanically, with only a few using sonic
devices. The tools measure diameter at a specific chord across the well. Since wellbores
are usually irregular, it is important to have a tool that measures diameter at several
different locations simultaneously. Such a tool is called a multi-finger caliper. Drilling
engineers or rig-site personnel use caliper measurement as a qualitative indication of both
the condition of the wellbore and the degree to which the mud system has maintained
hole stability. Caliper data are integrated to determine the volume of the open-hole,
which is then used in planning cementing operations.
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Circulation Valve (Circ Valve)
A Circulation Valve is a down-hole device that enables circulation through the tubing
string and associated annulus. As a completion accessory, a circulation valve is included
to circulate fluid for well kill or kickoff. Circulation valves typically are operated by
slick-line tools and are generally capable of several opening and closing cycles before
requiring service.
Collar
A threaded coupling used to join two lengths of pipe such as production tubing, casing or
liner. The type of thread and style of collar varies with the specifications and
manufacturer of the tubing.
Collar Locator
A down-hole tool or logging device used to detect and track (log) casing or tubing collars
across a zone of interest, typically for correlation purposes. Most collar locators detect
the magnetic anomaly created by the mass of the steel collar and transmit a signal to
surface-display and depth correlation equipment.
A Circulation Valve is a down-hole device that enables circulation through the
tubing string and associated annulus. As a completion accessory, a circulation valve is
included to circulate fluid for well kill or kickoff. Circulation valves typically are
operated by slick-line tools and are generally capable of several opening and closing
cycles before requiring service.
Crossover
A short subassembly used to enable two components with different thread types or sizes
to be connected.
Cross-flow
Cross-flow is the flow of reservoir fluids from one zone to another. Cross-flow can occur
when a lost returns event is followed by a well control event. The higher pressured
reservoir fluid flows out of the formation, travels along the wellbore to a lower pressured
formation, and then flows into the lower pressure formation.
Cross-flow is also another condition that exists when two production zones with
dissimilar pressure characteristics are allowed to communicate during production.
Reservoir fluid from the high-pressure zone will flow preferentially to the low-pressure
zone rather than up the production conduit unless the production parameters are closely
controlled.
Data Frac (Mini-Frac)
A small fracturing treatment performed before the main hydraulic fracturing treatment to
acquire critical job design and execution data and confirm the predicted response of the
treatment interval. The mini-frac procedure provides key design data from the parameters
associated with the injection of fluids and the subsequent pressure decline. The final job
procedures and treatment parameters are refined according to the results of the mini-frac
treatment.
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Down-hole Gauge
Is a pressure gauge, typically run on slick-line. Used to measure and record down-hole
pressure. Down-hole gauges are commonly used in assessing the down-hole pressure
under various flowing conditions, the basis of pressure transient analysis.
Dummy Valve
A blank gas-lift valve placed in a gas-lift mandrel to isolate the tubing string from the
annulus. Gas-lift valves frequently are replaced with dummy valves during intervention
work on wells with gas-lift completions.
Dump Bailer
A wire-line or slick-line tool used to place small volumes of cement slurry, or similar
material, in a wellbore. Typically, the slurry is placed on a plug or similar device that
provides a stable platform for the low-volume cement plug.
ESP (Electrical Submersible Pump)
Is an artificial-lift system that utilizes a down-hole pumping system that is electrically
driven by a pump. The pump typically comprises several staged centrifugal pump
sections that can be specifically configured to suit the production and wellbore
characteristics of a given application. Electrical submersible pump systems are a common
artificial-lift method, providing flexibility over a range of sizes and output flow
capacities.
ESP with pump monitor. Temperature, pressure, vibration, current-leakage and flow data
are measured by sensors down-hole and recorded by an integrated surface panel (ISP).
Falloff Test
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The measurement and analysis of pressure data taken after an injection well is shut in.
These data are often the easiest transient well-test data to obtain. Wellhead pressure rises
during injection, and if the well remains full of liquid after shut-in of an injector, the
pressure can be measured at the surface, and bottom-hole pressures can be calculated by
adding the pressure from the hydrostatic column to the wellhead pressure. Since most
water-injection wells are fractured during injection, and injection wells often go on
vacuum, the fluid level can fall below the surface. Dealing with this complication
requires reverting to bottom-hole pressure gauges or sonic devices.
Fish
Anything left in a wellbore. It does not matter whether the fish consists of junk metal, a
hand tool, a length of drill-pipe or drill collars, or running tools left by service companies.
Once the component is lost, it is properly referred to as simply "the fish." Typically,
anything put into the hole is accurately measured and sketched, so that appropriate
fishing tools can be selected if the item must be fished out of the hole.
Fishing Diagram
Is a diagram noting the major profiles and dimensions of tools and equipment run into a
well-bore. A fishing diagram should be prepared for every tool operation, enabling
contingency plans to be implemented efficiently if the tool string becomes stuck or lost.
Fishing Neck
The surface on which a fishing tool engages when retrieving tubing, tools or equipment
stuck or lost in a wellbore. Tools and equipment that are temporarily installed in a
wellbore are generally equipped with a specific fishing-neck profile to enable the running
and retrieval tools to reliably engage and release.
Fishing Tool
A general term for special mechanical devices used to aid the recovery of equipment lost
down-hole. These devices generally fall into four classes: diagnostic, inside grappling,
outside grappling, and force intensifiers or jars. Diagnostic devices may range from a
simple impression block made in a soft metal, usually lead, that is dropped rapidly onto
the top of the fish so that upon inspection at the surface, the fisherman may be able to
custom design a tool to facilitate attachment to and removal of the fish. Other diagnostic
tools may include electronic instruments and even down-hole sonic or visual-bandwidth
cameras. Inside grappling devices, usually called spears, generally have a tapered and
threaded profile, enabling the fisherman to first guide the tool into the top of the fish, and
then thread the fishing tool into the top of the fish so that recovery may be attempted.
Outside grappling devices, usually called over-shots, are fitted with threads or another
shape that "swallows" the fish and does not release it as it is pulled out of the hole. Overshots are also fitted with a crude drilling surface at the bottom, so that the overshot may
be lightly drilled over the fish, sometimes to remove rock or metallic junk that may be
part of the sticking mechanism. Jars are mechanical down-hole hammers, which enable
the fisherman to deliver high-impact loads to the fish, far in excess of what could be
applied in a quasi-static pull from the surface.
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Flange
A connection profile used in pipe work and associated equipment to provide a means of
assembling and disassembling components. Most oilfield flanges feature a bolt-hole
pattern to allow the joint to be secured and a gasket profile to ensure a pressure-tight seal.
The design and specification of a flange relates to the size and pressure capacity of the
equipment to which it is fitted.
Flapper Valve
A check valve that has a spring-loaded plate (or flapper) that may be pumped through,
generally in the down-hole direction, but closes if the fluid attempts to flow back through
the drill-string to the surface. This reverse flow might be encountered either due to a Utube effect when the bulk density of the mud in the annulus is higher than that inside the
drill-pipe, or a well control event.
Safety-valve curved flapper. The curved flapper design allows a larger inside diameter
for the production conduit. The wings of the flapper are profiled to fit within a smaller
radius than would be possible with a conventional flat-flapper design. This can offer
important advantages when wellbore or safety-valve geometry is critical.
Flash Point
Is the lowest temperature at which an application of a flame to the test chamber of a tester
causes vapors of the sample in the chamber to ignite. The test can be applied to base
fluids being considered for any flammable liquid to determine at what temperature an
explosion hazard exists. Test methods, established by API and ASTM, include open-cup
and closed-cup tests.
Flow Back
The process of allowing fluids to flow from the well following a treatment, either in
preparation for a subsequent phase of treatment or in preparation for clean-up and
returning the well to production.
Flow Test
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A test performed to ensure stable well conditions or the integrity of a plug, valve or flowcontrol device. In most cases, the flow check involves observing stable fluid levels or
conditions for a prescribed period.
Flow-line
A flow-line refers to any surface pipeline carrying oil, gas or water that connects the
wellhead to a manifold or to production facilities.
Frac Job (Hydraulic Fracturing)
A stimulation treatment routinely performed on oil and gas wells in low-permeability
reservoirs. Specially engineered fluids are pumped at high pressure and rate into the
reservoir interval to be treated, causing a vertical fracture to open. The wings of the
fracture extend away from the wellbore in opposing directions according to the natural
stresses within the formation. Proppant, such as grains of sand of a particular size, is
mixed with the treatment fluid to keep the fracture open when the treatment is complete.
Hydraulic fracturing creates high-conductivity communication with a large area of
formation and bypasses any damage that may exist in the near-wellbore area.
Fracing is the process of pumping into a closed wellbore with powerful hydraulic pumps
to create enough down-hole pressure to crack or fracture the formation. This allows
injection of proppant into the formation, thereby creating a plane of high-permeability
sand through which fluids can flow. The proppant remains in place once the hydraulic
pressure is removed and therefore props open the fracture and enhances flow into the
wellbore.
Full Bore
A description of the internal area and surfaces of a tool or tubular assembly through
which there is an unimpeded internal diameter. In some cases, full-bore is used to
describe the form of a nominal internal diameter that extends over the length of the tool
or interval without any variation. In other applications, the term simply implies an ability
to pass a ball or similar item of a stated drift diameter through the assembly.
Gas Lift Mandrel
A gas-lift system component that is assembled with the production tubing string to
provide a means of locating gas-lift valves. The position or depth of the gas lift valves is
crucial to the efficient operation of the entire system. Consequently, proper assembly of
the gas lift mandrels within the completion tubulars is essential. A port in the gas-lift
mandrel provides communication between the lift-gas supply in the tubing annulus and
the production-tubing conduit.
Gauge Ring
A precisely machined test device, typically fabricated from steel or similar durable
material, having a specified internal or external diameter. The gauge ring is used to
confirm the dimensional compatibility of tools and equipment that must pass through
restrictions of a certain diameter.
Grease Head (E-line Pack-off)
An assembly of components used to contain wellhead fluids and pressure during braidedline or electric wire-line operations. The braided line or electric wire-line passes through
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a close-tolerance tube assembly as it leaves the wellbore. High-pressure grease is pumped
into the surrounding annulus to create a pressure-tight dynamic seal that is maintained
during the operation by injecting more grease as required. A slight leakage of grease is
normal, and the addition of fresh grease enables the consistency of the seal to be
maintained at an effective level.
Header
Is a pipe arrangement in a gathering system that connects flow-lines from several
wellheads into a single gathering line. A header has production and testing valves to
control the flow of each well, thus directing the produced fluids to production or testing
vessels.
Individual gas/oil ratios and well production rates of oil, gas and water can be assigned
by opening and closing selected valves in a header and using individual metering
equipment or separators.
Injection Mandrel
Is a down-hole completion component that enables injection of treatment chemicals or
inhibitors into the production conduit. The injection mandrel is equipped with a port- and
check-valve system to direct fluid pumped down the annulus or injection line into the
production conduit.
Junk Basket
Anything in the wellbore that is not supposed to be there. The term is usually reserved for
small pieces of steel such as hand tools, small parts, bit nozzles, pieces of bits, or other
down-hole tools, and remnants of milling operations.
Kill
Is how to stop a well from flowing or having the ability to flow into the well-bore. Kill
procedures typically involve circulating reservoir fluids out of the wellbore or pumping
higher density mud into the wellbore, or both. In the case of an induced kick, where the
mud density is sufficient to kill the well but the reservoir has flowed as a result of pipe
movement, the driller must circulate the influx out of the wellbore. In the case of an
underbalanced kick, the driller must circulate the influx out and increase the density of
the drilling fluid. In the case of a producing well, a kill fluid with sufficient density to
overcome production of formation fluid is pumped into the well to stop the flow of
reservoir fluids.
Light Crude
Is crude oil that has a high API gravity, usually more than 40o.
Liner
Any string of casing in which the top does not extend to the surface but instead is
suspended from inside the previous casing string. Many conventional well designs
include a production liner set across the reservoir interval. This reduces the cost of
completing the well and allows some flexibility in the design of the completion in the
upper wellbore, such as when the fluid characteristics make it beneficial to increase the
diameter of the conduit and components.
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Casing strings with liner
Live Oil
Is oil containing dissolved gas in solution that may be released from solution at surface
environmental conditions. Live oil must be handled and pumped under closely controlled
conditions to avoid the risk of explosion or fire.
Lubricator
A term initially applied to the assembly of pressure-control equipment used on slick-line
operations to house the tool string in preparation for running into the well or for retrieval
of the tool string on completion of the operation. The lubricator is assembled from
sections of heavy-wall tube generally constructed with integral seals and connections.
Lubricator sections are routinely used on the assembly of pressure-control equipment for
other well-intervention operations such as wire-line (E-line), and coiled tubing.
A long, high-pressure pipe fitted to the top of a wellhead or Christmas tree so that tools
may be put into a high-pressure well. The top of the lubricator assembly includes a highpressure grease-injection section and sealing elements. The lubricator is installed on top
of the tree and tested, the tools placed in the lubricator and the lubricator pressurized to
wellbore pressure. Then the top valves of the tree are opened to enable the tools to fall or
be pumped into the wellbore under pressure. To remove the tools, the reverse process is
used: the tools are pulled up into the lubricator under wellbore pressure, the tree valves
are closed, the lubricator pressure is bled off, and then the lubricator may be opened to
remove the tools.
Mandrel
Is a bar, shaft or spindle around which other components are arranged or assembled. The
term has been extended in oil and gas well terminology to include specialized tubular
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components that are key parts of an assembly or system, such as gas-lift mandrel or
packer mandrel.
Manifold
An arrangement of piping or valves designed to control, distribute and often monitor fluid
flow. Manifolds are often configured for specific functions, such as a choke manifold
used in well-control operations and a squeeze manifold used in squeeze-cementing work.
In each case, the functional requirements of the operation have been addressed in the
configuration of the manifold and the degree of control and instrumentation required.
Maximum Treating Pressure
Maximum Treating Pressure is the surface-pump pressure limit below which a treatment
should be performed. The maximum treating pressure is determined to avoid fracturing
the formation or damaging completion components. The maximum treating pressure is
generally calculated to ensure that the pump-pressure limit equates to down-hole and
reservoir conditions that are within the design limits of the treatment.
Mechanical Jar
A type of jar that incorporates a mechanical trip or firing mechanism that activates only
when the necessary tension or compression has been applied to the running string. In
slick-line operations, the term is often used to describe any jar that does not contain a
hydraulic trip mechanism, such as link and tubular jars that do not incorporate a firing
mechanism.
Memory Gauge
A type of electronic pressure gauge that samples and records down-hole pressures, with
the data being stored, ready for downloading to acquisition equipment when the tool
assembly has been retrieved to surface. Memory gauges are generally used to measure
bottom-hole pressures and temperatures in response to various production rates in tests to
assess well productivity and reservoir performance.
Methane
Methane is the lightest and most abundant of the hydrocarbon gases and the principal
component of natural gas. Methane is a colorless, odorless gas that is stable under a wide
range of pressure and temperature conditions in the absence of other compounds.
Mill
Is a tool that grinds metal down-hole. A mill is usually used to remove junk in the hole or
to grind away all or part of a casing string. In the case of junk, the metal must be broken
into smaller pieces to facilitate removal from the wellbore so that drilling can continue.
When milling casing, the intent is to cut a window through the side of the casing or to
remove a continuous section of the casing so that the wellbore may be deviated from the
original well through the window or section removed. Depending on the type of grinding
or metal removal required, the shape of the cutting structures of mills varies. Virtually all
mills, however, utilize tungsten carbine cutting surfaces.
Mill Shoe
A down-hole tool routinely used in fishing operations to prepare the top and outside
surface of a fish, generally to allow an overshot or similar fishing tool to engage cleanly
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on the fish. In some cases, the outer portion of a fish may be milled out to allow the body
and remaining debris to be pushed to the bottom of the wellbore.
Milling
The use of a mill or similar down-hole tool to cut and remove material from equipment or
tools located in the wellbore. Successful milling operations require appropriate selection
of milling tools, fluids and techniques. The mills, or similar cutting tools, must be
compatible with the fish materials and wellbore conditions. The circulated fluids should
be capable of removing the milled material from the wellbore. Finally, the techniques
employed should be appropriate to the anticipated conditions and the likely time required
to reach the operation objectives.
Minimum Restriction
The smallest diameter present in a wellbore through which a tool string must pass to
enable access to the operating depth or zone of interest. The minimum restriction
determines the maximum tool string outside diameter and may influence the
configuration of the assembled tools or equipment. The minimum restriction should be
considered in both running and retrieving modes if any increase in tool string outside
diameter is likely, such as when perforating or when using inflatable packers.
Miscible
Phases that can mix and form a homogeneous mixture. Hydrocarbon gases and liquids
are commonly miscible.
Miscible Displacement
Miscible is a general term for injection processes that introduce miscible gases into the
reservoir. A miscible displacement process maintains reservoir pressure and improves oil
displacement because the interfacial tension between oil and water is reduced. The effect
of gas injection is similar to that of a solution gas-drive.
Miscible displacement is a major branch of enhanced oil recovery processes. Injected
gases include liquefied petroleum gas (LPG), such as propane, methane under high
pressure, methane enriched with light hydrocarbons, nitrogen under high pressure, and
carbon dioxide [CO2] under suitable reservoir conditions of temperature and pressure.
The fluid most commonly used for miscible displacement is carbon dioxide because it
reduces the oil viscosity and is less expensive than liquefied petroleum gas.
Miscible displacement is also called miscible gas-drive, miscible drive or miscible flood.
Natural Gas
A naturally occurring mixture of hydrocarbon gases that is highly compressible and
expansible. Methane [CH4] is the chief constituent of most natural gas (constituting as
much as 85% of some natural gases), with lesser amounts of ethane [C2H6], propane
[C3H8], butane [C4H10] and pentane [C5H12]. Impurities can also be present in large
proportions, including carbon dioxide, helium, nitrogen and hydrogen sulfide.
Natural Gas Liquids
Components of natural gas that are liquid at surface in field facilities or in gas-processing
plants. Natural gas liquids can be classified according to their vapor pressures as low
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(condensate), intermediate (natural gasoline) and high (liquefied petroleum gas) vapor
pressure.
Natural gas liquids include propane, butane, pentane, hexane and heptane, but not
methane and ethane, since these hydrocarbons need refrigeration to be liquefied. The
term is commonly abbreviated as NGL.
Naturally Flowing Well
Is a well in which the formation pressure is sufficient to produce oil at a commercial rate
without requiring a pump. Most reservoirs are initially at pressures high enough to allow
a well to flow naturally.
Neutral Point
The point on a string of tubulars at which point there are neither tension nor compression
forces present. Below the neutral point, there will be compression forces that build
toward the bottom of the wellbore. Above the neutral point, tensile forces build to a
maximum applied at the hanger or as hook load.
Nipple
A completion component fabricated as a short section of heavy wall tubular with a
machined internal surface that provides a seal area and a locking profile. Landing nipples
are included in most completions at predetermined intervals to enable the installation of
flow-control devices, such as plugs and chokes. Three basic types of landing nipple are
commonly used: no-go nipples, selective-landing nipples and ported or safety-valve
nipples.
Nitrogen Cushion
A column of high-pressure nitrogen typically applied to a tubing string in preparation for
drill-stem testing or perforating operations in which the reservoir formation is to be
opened to the tubing string. The nitrogen cushion allows a precise pressure differential to
be applied before opening flow from the reservoir. Once flow begins, the nitrogen
cushion pressure can be easily and safely bled down to flow formation fluids under a high
degree of control.
Perforating Gun (E-line)
A device used to perforate oil and gas wells in preparation for production. Containing
several shaped explosive charges, perforating guns are available in a range of sizes and
configurations. The diameter of the gun used is typically determined by the presence of
wellbore restrictions or limitations imposed by the surface equipment.
Nitrogen Lift
The use of nitrogen gas circulated into the production conduit to displace liquids and
reduce the hydrostatic pressure created by the fluid column. Nitrogen lifting is a common
technique used to initiate production on a well following work-over or overbalanced
completion. A coiled tubing string is generally used to apply the treatment, which
involves running to depth while pumping high-pressure nitrogen gas. Once the kill-fluid
column is unloaded and the well is capable of natural flow, the coiled tubing string is
removed and the well is prepared for production.
Nitrogen Unit
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A high-pressure pump or compressor unit capable of delivering high-purity nitrogen gas
for use in oil or gas wells. Two basic types of unit are commonly available: a nitrogen
converter unit that pumps liquid nitrogen at high pressure through a heat exchanger or
converter to deliver high-pressure gas at ambient temperature, and a nitrogen generator
unit that compresses and separates air to provide a supply of high-pressure nitrogen gas.
No-go Landing Nipple
A nipple that incorporates a reduced diameter internal profile that provides a positive
indication of seating by preventing the tool or device to be set from passing through the
nipple. In many completions, a no-go landing nipple is preferred for the deepest nipple
location, providing a no-go barrier to protect against a tool string being run or dropped
below the tubing string.
No-go Nipple
Noise Log (E-Line)
A record of the sound measured at different positions in the borehole. Since fluid
turbulence generates sound, high noise amplitudes indicate locations of greater
turbulence such as leaks, channels and perforations. Noise logging is used primarily for
channel detection, but has also been used to measure flow rates, identify open
perforations, detect sand production and locate gas-liquid interfaces. The log may be
either a continuous record against depth or a series of stationary readings. The log may
indicate the total signal over all frequencies, the signal at a single frequency, or consist of
a set of logs for different frequency ranges. Different frequency ranges can be tied to
different sources of noise or different flow regimes.
Although first introduced around 1955, the technique was not used commercially until
after laboratory studies in the early 1970s
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O-ring
A type of circular seal commonly found in down-hole tools and a wide range of surface
equipment applications. The specification of O-ring material depends on the conditions
for which the seal is intended, such as system operating temperature and pressure.
Various backup systems are used to support the O-ring seal in either dynamic or static
sealing applications.
Off-pattern Well
Is a production or injection well that has a lateral or diagonal displacement with respect
to the other wells in an injection pattern formation. The existence of an off-pattern well
affects oil recovery and water/oil ratio.
Pack-Off
Pack-off is a means to effect hydraulic isolation, either with a sealing device, such as a
packer, or with a specialized plastic or fluid, such as a sealing compound.
Packer
A Packer is a down-hole device used in almost every “Completion” to isolate the annulus
from the production conduit, enabling controlled production, injection or treatment. A
typical packer assembly incorporates a means of securing the packer against the casing or
liner wall, such as a slip arrangement, and a means of creating a reliable hydraulic seal to
isolate the annulus, typically by means of an expandable elastomeric element. Packers are
classified by application, setting method and possible retrievability.
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Paraffin
Paraffin is a hydrocarbon compound that often precipitates on production components as
a result of the changing temperatures and pressures within the production system. Heavy
paraffin is a wax-like substance that may build up on the completion components and
will, if severe, restrict production.
Paraffin Control
A set of techniques used to prevent or considerably reduce paraffin deposition. Paraffin
control might involve the following options:
- use of paraffin inhibitors.
- maintaining pipe surfaces in a water-wet condition because paraffin will not adhere to
water. However, the presence of natural surfactants in some crude oils converts water-wet
surfaces to an oil-wet condition, making this technique effective only temporarily.
- coating the pipe with plastic to provide a smooth surface and reduce paraffin adhesion.
- reducing heat transfer to maintain the oil temperature above its cloud point. Filling the
annulus of a well with a fluid that has poorer heat transfer properties than the oil
maintains the temperature of the flowing crude oil above its cloud point.
Paraffin is normally found in the tubing close to surface in the arctic environment.
Nevertheless, it can form at the perforations, or even inside the formation, especially in
depleted reservoirs or reservoirs under gas-cycling conditions.
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Paraffin Scratcher (Cutter)
A down-hole tool, generally run on slick-line, used to remove paraffin and soft wax
deposits from the internal wall of production tubulars and completion equipment.
Perforate
To perforate is to create holes in the casing or liner to achieve efficient communication
between the reservoir and the wellbore. The characteristics and placement of the
communication paths (perforations) can have significant influence on the productivity of
the well. Therefore, a robust design and execution process should be followed to ensure
efficient creation of the appropriate number, size and orientation of perforations. A
perforating gun assembly with the appropriate configuration of shaped explosive charges
and the means to verify or correlate the correct perforating depth can be deployed on
wire-line, tubing or coiled tubing.
Perforating Charge
An explosive device that utilizes a cavity-effect explosive reaction to generate a highpressure, high-velocity jet that creates a perforation tunnel. The shape of the explosive
material and powdered metal lining determine the shape of the jet and performance
characteristics of the charge. The extremely high pressure and velocity of the jet cause
materials, such as steel, cement and rock formations, to flow plastically around the jet
path, thereby creating the perforation tunnel.
Perforating Gun
A device used to perforate oil and gas wells in preparation for production. Containing
several shaped explosive charges, perforating guns are available in a range of sizes and
configurations. The diameter of the gun used is typically determined by the presence of
wellbore restrictions or limitations imposed by the surface equipment.
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Perforated Interval
Is the section of wellbore that has been prepared for production by creating channels
between the reservoir formation and the well-bore. In many cases, long reservoir sections
will be perforated in several intervals, with short sections of unperforated casing between
each interval to enable isolation devices, like packers, to be set for subsequent treatments
or remedial operations.
Perforated Liner
A wellbore tubular in which slots or holes have been made before the string is assembled
and run into the wellbore. Perforated liners typically are used in small-diameter wellbores
or in sidetracks within the reservoir where there is no need for the liner to be cemented in
place, as is required for zonal isolation.
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Permafrost (Alaska, North Slope)
In geology, permafrost or permafrost soil is soil at or below the freezing point of water (0
°C or 32 °F) for two or more years. Ice is not always present, as may be in the case of
nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the
potential hydraulic saturation of the ground material. Most permafrost is located in high
latitudes (i.e. land in close proximity to the North and South poles), but alpine permafrost
may exist at high altitudes in much lower latitudes. Permafrost accounts for 0.022% of
total water and exists in 24% of exposed land in the Northern Hemisphere.
On the North Slope, permafrost ranges in thickness from about 700 to as much as 2,240
feet thick, and may be as cold as minus 8 to minus 10 degrees C.
Permeability
Is the ability, or measurement of a rock's ability, to transmit fluids, typically measured in
“darcies” or “millidarcies”. Formations that transmit fluids readily, such as sandstones,
are described as permeable and tend to have many large, well-connected pores.
Impermeable formations, such as shale and siltstones, tend to be finer grained or of a
mixed grain size, with smaller, fewer, or less interconnected pores. Absolute permeability
is the measurement of the permeability conducted when a single fluid, or phase, is present
in the rock. Effective permeability is the ability to preferentially flow or transmit a
particular fluid through a rock when other immiscible fluids are present in the reservoir
(for example, effective permeability of gas in a gas-water reservoir). The relative
saturations of the fluids as well as the nature of the reservoir affect the effective
permeability. Relative permeability is the ratio of effective permeability of a particular
fluid at a particular saturation to absolute permeability of that fluid at total saturation. If a
single fluid is present in a rock, its relative permeability is 1.0. Calculation of relative
permeability allows for comparison of the different abilities of fluids to flow in the
presence of each other, since the presence of more than one fluid generally inhibits flow.
Pigging
The act of forcing a device called a pig through a pipeline for the purposes of displacing
or separating fluids, and cleaning or inspecting the line.
A “Pig” is a device with blades or brushes inserted in a pipeline for cleaning purposes.
The pressure of the oil stream behind pushes the pig along the pipeline to clean out rust,
wax, scale and debris. These devices are also called scrapers.
Pipe Stretch
Pipe Stretch is the increase in length resulting from the combination of forces acting on a
string within the wellbore. The principal factors resulting in an increase in string length
are the weight of the string itself and the effects of thermal expansion.
Pitting
Is a type of corrosion in which there is loss of metal in localized areas. The corrosion rate
in the pits is many times greater than the corrosion rate on the entire surface.
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The resultant pits can be large and shallow or narrow and deep. Pitting is a more
dangerous problem than general corrosion because the pitted areas can be easily
penetrated.
Plug and Abandon
To prepare a well to be closed permanently, usually after either logs determine there is
insufficient hydrocarbon potential to complete the well, or after production operations
have drained the reservoir. Different regulatory bodies have their own requirements for
plugging operations. Most require that cement plugs be placed and tested across any open
hydrocarbon-bearing formations, across all casing shoes, across freshwater aquifers, and
perhaps several other areas near the surface, including the top 20 to 50 ft [6 to 15 m] of
the wellbore. The well designer may choose to set bridge plugs in conjunction with
cement slurries to ensure that higher density cement does not fall in the wellbore. In that
case, the bridge plug would be set and cement pumped on top of the plug through drillpipe, and then the drill-pipe withdrawn before the slurry thickened.
Positive-displacement Pump
Is a type of fluid pump in which the displacement volume of the pump is fixed for each
rotation of the pump. Generally associated with high-pressure applications, positivedisplacement pumps are commonly used in drilling operations to circulate the drilling
fluid and in a range of oil and gas well treatments, such as cementing, matrix treatments
and hydraulic fracturing.
Production Log
Is a record of one or more in-situ measurements that describe the nature and behavior of
fluids in or around the borehole during production or injection. Production logs are run
for the purpose of analyzing dynamic well performance and the productivity or injectivity
of different zones, diagnosing problem wells, or monitoring the results of a stimulation or
completion. The term is sometimes extended to include logs run to measure the physical
condition of the well, for example cement bond and corrosion logs.
The earliest production logs consisted of temperature logs (1930s) and flow-meters
(1940s), to which were soon added fluid-density and capacitance logs (1950s). Flow-rate
measurements were gradually improved by the development of tracer logs and
improvement to the basic spinner flow-meter.
These techniques were adequate for near-vertical wells with single or biphasic flow, but
could be misleading in highly deviated, and especially horizontal, wells. New techniques
were developed starting in the 1980s. These techniques focused on local probes to
measure holdup at different points in the borehole, nuclear techniques to analyze the total
holdup of all three phases, and phase-velocity logs for the analysis of individual fluids. At
the same time, complex flow structures and flow regimes have been studied more
extensively using flow loops.
Production Packer
A device used to isolate the annulus and anchor or secure the bottom of the production
tubing string. A range of production packer designs is available to suit the wellbore
geometry and production characteristics of the reservoir fluids.
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Production String
Is the primary conduit through which reservoir fluids are produced to surface. The
production string is typically assembled with tubing and completion components in a
configuration that suits the wellbore conditions and the production method. An important
function of the production string is to protect the primary wellbore tubing, including the
casing and liner, from corrosion or erosion by the reservoir fluid.
Proppant
Sized particles mixed with fracturing fluid to hold fractures open after a hydraulic
fracturing treatment. In addition to naturally occurring sand grains, man-made or
specially engineered proppants, such as resin-coated sand or high-strength ceramic
materials like sintered bauxite, may also be used. Proppant materials are carefully sorted
for size and sphericity to provide an efficient conduit for production of fluid from the
reservoir to the wellbore.
Pulling Tool
Is a slick-line or coiled tubing tool used to retrieve temporary devices, such as plugs and
flow-control equipment, from the wellbore. Pulling tools are available in a range of sizes
and profiles and must be compatible with the equipment to be retrieved. A contingency
release system in the pulling tool allows the tool to be released and retrieved if the
equipment to be retrieved cannot be released.
Retrievable Bridge Plug
A type of down-hole isolation tool that may be unset and retrieved from the wellbore
after use, such as may be required following treatment of an isolated zone. A retrievable
bridge plug is frequently used in combination with a packer to enable accurate placement
and injection of stimulation or treatment fluids.
Surface Safety Valve (SSV)
Surface safety valve (SSV) is a hydraulically actuated fail-safe gate valve for producing
or testing oil and gas wells with high flow rates, high pressures, or the presence of H2S.
The SSV is used to quickly shut down the well upstream in the event of overpressure,
failure, a leak in downstream equipment, or any other well emergency requiring an
immediate shut down.
SSV is remotely operated by an emergency shutdown device (ESD), which can be
triggered automatically by high or low pressure pilot actuators. If an emergency occurs,
this feature reduces the possibility of personnel injuries.
A number of SSV models are available for different well conditions (pressures,
temperatures, and flow rates) and with various connections, such as hammer union or
API-6A flanges.
All SSVs are manufactured under Type Approval or Design Verification Review and
provided with a Certificate of Conformity and full quality file.
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Sub Surface Safety Valve
A downhole safety valve refers to a component on an oil and gas well, which acts as a
failsafe to prevent the uncontrolled release of reservoir fluids in the event of a worst case
scenario surface disaster. It is almost always installed as a vital component on the
completion. These valves are commonly uni-directional flapper valves which open
downwards, such that the flow of wellbore fluids try to push it shut, while pressure from
surface pushes it open. This means that when closed, it will isolate the reservoir fluids
from surface. Most downhole safety valves are controlled hydraulically from surface,
meaning they are opened using a hydraulic connection linked directly to a well control
panel.
They function when hydraulic pressure is applied down a control line. The hydraulic
pressure forces a sleeve within the valve to slide downwards. This movement compresses
a large spring and pushes the flapper downwards to open the valve. When hydraulic
pressure is removed, the spring pushes the sleeve back up and causes the flapper to shut.
In this way, it is failsafe and will isolate the wellbore in the event of a loss of the
wellhead. The full designation for a typical valve is 'tubing retrievable, surface
controlled, subsurface safety valve', abbreviated to TR-SCSSV.
Sub Surface Safety Valve (Control Line)
A small-diameter hydraulic line used to operate down-hole completion equipment such as
the surface controlled subsurface safety valve (SCSSV). Most systems operated by
control line operate on a fail-safe basis. In this mode, the control line remains pressurized
at all times. Any leak or failure results in loss of control line pressure, acting to close the
safety valve and render the well safe.
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Torque Flow-meter
A device for measuring in situ the velocity of fluid flow in a production or injection well
based on the torque, or force, produced by the fluid on a stationary impeller. This torque
can be related to the effective velocity of flow across the impeller. The torque flow-meter
is sometimes used as an alternative to the spinner flow-meter.
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Down-hole Terms
API
Abbreviation for American Petroleum Institute, a trade association founded in 1919 with
offices in Washington, DC, USA. The API is sponsored by the oil and gas industry and is
recognized worldwide. Among its long-term endeavors is the development of
standardized testing procedures for drilling equipment, drilling fluids and cements, called
API Recommended Practices ("RPs"). The API licenses the use of its monogram (logo),
monitors supplier quality assurance methods and sets minimum standards for materials
used in drilling and completion operations, called API Specifications ("Specs"). The API
works in conjunction with the International Organization of Standards (ISO).
Artificial Lift
Any system that adds energy to the fluid column in a wellbore with the objective of
initiating and improving production from the well. Artificial-lift systems use a range of
operating principles, including rod pumping, gas lift and electric submersible pump.
Asphaltenes
Organic materials consisting of aromatic and naphthenic ring compounds containing
nitrogen, sulfur and oxygen molecules. The asphaltene fraction of crude is defined as the
organic part of the oil that is not soluble in straight-chain solvents such as pentane or
heptane.
Asphaltenes exist as a colloidal suspension stabilized by resin molecules (aromatic ring
systems) in the oil. The stability of asphaltic dispersions depends on the ratio of resin to
asphaltene molecules. The determination of the quantity of resin is important in
estimating the potential damage created by asphaltenes.
Asphaltene precipitates as a result of pressure drop, shear (turbulent flow), acids, solution
carbon dioxide [CO2], injected condensate, mixing of incompatible crude oils or other
conditions or materials that break the stability of the asphaltic dispersion. For example, in
matrix acidizing, iron ions in solution favor the precipitation of asphaltene deposits.
Bottom-hole Injection Pressure (BHIP)
The down-hole pressure at which a treatment fluid can be injected into a zone of interest.
The bottom-hole injection pressure is typically calculated by adding the hydrostatic
pressure of the fluid column to the surface pump pressure measured during an injection
test.
Bottom-hole Shut-in
A well shut in slightly above the producing formation by use of special down-hole tools
containing a valve that can be preprogrammed or controlled from the surface. This
practice is commonly associated with drill-stem tests. Technology exists to employ
bottom-hole shut-in in suitably equipped completed wells.
Bottom-hole Temperature
The temperature in the borehole at total depth at the time it is measured. In log
interpretation, the bottom hole temperature (BHT) is taken as the maximum recorded
temperature during a logging run, or preferably the last of series of runs during the same
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operation. BHT is the temperature used for the interpretation of logs at total depth.
Farther up the hole, the correct temperature is calculated by assuming a certain
temperature gradient. The BHT lies between the bottom-hole circulating temperature
(BHCT) and the bottom-hole static temperature (BHST).
Breakdown Pressure
The pressure at which the rock matrix of an exposed formation fractures and allows fluid
to be injected. The breakdown pressure is established before determining reservoir
treatment parameters. Hydraulic fracturing operations are conducted above the
breakdown pressure, while matrix stimulation treatments are performed with the
treatment pressure safely below the breakdown pressure.
British Thermal Unit (BTU)
A measure of heat energy required to raise the temperature of one pound of water by one
degree Fahrenheit. British thermal unit is abbreviated as BTU.
Bullhead
To forcibly pump fluids into a formation, usually formation fluids that have entered the
wellbore during a well control event. Though bull-heading is intrinsically risky, it is
performed if the formation fluids are suspected to contain hydrogen sulfide gas to prevent
the toxic gas from reaching the surface. Bull-heading is also performed if normal
circulation cannot occur, such as after a borehole collapse. The primary risk in bullheading is that the drilling crew has no control over where the fluid goes and the fluid
being pumped down-hole usually enters the weakest formation. In addition, if only
shallow casing is cemented in the well, the bull-heading operation can cause wellbore
fluids to broach around the casing shoe and reach the surface. This broaching to the
surface has the effect of fluidizing and destabilizing the soil (or the subsea floor), and can
lead to the formation of a crater and loss of equipment and life.
Caliper Log
A representation of the measured diameter of a borehole along its depth. Caliper logs are
usually measured mechanically, with only a few using sonic devices. The tools measure
diameter at a specific chord across the well. Since wellbores are usually irregular
(rugose), it is important to have a tool that measures diameter at several different
locations simultaneously. Such a tool is called a multi-finger caliper. Drilling engineers
or rig-site personnel use caliper measurement as a qualitative indication of both the
condition of the wellbore and the degree to which the mud system has maintained hole
stability. Caliper data are integrated to determine the volume of the open-hole, which is
then used in planning cementing operations.
Carbonate Scale
A common type of mineral deposit that is often found on wellbore tubulars and
components as the saturation of produced water is affected by changing temperature and
pressure conditions in the production conduit. Carbonate scales have a high dissolution
rate in common oilfield acids and generally can be effectively removed using acid or
chemical treatments. Scale inhibition techniques also may be used to prevent scale
formation. In the majority of cases, scale prevention is simpler and more cost-effective
than attempting a cure.
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Circulate Out (Drilling)
To pump the drilling fluid until a sample from the bottom of the hole reaches the surface.
This is commonly performed when drilling has ceased so that the well-site geologist may
collect a cuttings sample from the formation being drilled, or when the driller suspects
that a small amount of gas has entered the wellbore. Thus, by circulating out, the gas
bubble is eased out of the wellbore safely.
Clean-out
Is the removal of wellbore-fill material, such as sand, scale or organic materials, and
other debris from the well-bore. Many reservoirs produce some sand or fines that may not
be carried to surface in the produced fluid. Accumulations of fill material may eventually
increase in concentration within the lower wellbore, possibly restricting production.
Cleanouts using coiled tubing, snubbing or hydraulic work-over techniques are
performed routinely.
Coiled Tubing Unit
The package of equipment required to run a coiled tubing operation. Four basic
components are required: the coiled tubing reel to store and transport the coiled tubing
string, the injector head to provide the tractive effort to run and retrieve the coiled tubing
string, the control cabin from which the equipment operator controls and monitors the
operation, and the power pack that generates the necessary hydraulic and pneumatic
power required by the other components. The dimensions and capacities of the coiled
tubing unit components determine the size and length of coiled tubing string that can be
used on the unit. Pressure-control equipment is incorporated into the equipment to
provide the necessary control of well pressure fluid during normal operating conditions
and contingency situations requiring emergency control.
Collapse Pressure
The pressure at which a tube, or vessel, will catastrophically deform as a result of
differential pressure acting from outside to inside of the vessel or tube. The collapsepressure rating of perfectly round tubing is relatively high. However, when the tubing is
even slightly oval, the differential pressure at which the tube will collapse may be
significantly reduced. This is an important factor in determining the operating limits of
coiled tubing strings since the action of spooling the string tends to induce some ovality.
Deviation
Is the angle at which a wellbore diverges from vertical. Wells can deviate from vertical
because of the dips in the beds being drilled through. Wells can also be deliberately
deviated by the use of a whip-stock or other steering mechanism. Wells are often
deviated or turned to a horizontal direction to increase exposure to producing zones,
intersect a larger number of fractures, or to follow a complex structure.
Differential Pressure
In general, a measurement of fluid force per unit area (measured in units such as pounds
per square in.) subtracted from a higher measurement of fluid force per unit area. This
comparison could be made between pressures outside and inside a pipe, a pressure vessel,
before and after an obstruction in a flow path, or simply between two points along any
fluid path, such as two points along the inside of a pipe or across a packer.
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It can also be the difference between two pressure measurements. For production
wells, the differential pressure is the difference between average reservoir pressure and
bottom-hole pressure, and for injection wells, it is the difference between injection
pressure and average reservoir pressure.
Dry Gas
Gas produced from a well that produces little or no condensate or reservoir liquids. The
production of liquids from gas wells complicates the design and operation of surface
process facilities required to handle and export the produced gas.
Duel Completion
Is a single wellbore having tubulars and equipment that enable production from two
segregated zones. In most cases, two tubing strings will be used to provide the necessary
level of control and safety for the fluids from both zones. However, in some simple dual
completions, the second or upper zone is produced up the tubing-casing annulus.
Fish
Anything left in a wellbore. It does not matter whether the fish consists of junk metal, a
hand tool, a length of drill-pipe or drill collars, or running tools left by service companys.
Once the component is lost, it is properly referred to as simply "the fish." Typically,
anything put into the hole is accurately measured and sketched, so that appropriate
fishing tools can be selected if the item must be fished out of the hole.
Full Bore
A description of the internal area and surfaces of a tool or tubular assembly through
which there is an unimpeded internal diameter. In some cases, full-bore is used to
describe the form of a nominal internal diameter that extends over the length of the tool
or interval without any variation. In other applications, the term simply implies an ability
to pass a ball or similar item of a stated drift diameter through the assembly.
Full Bore
A description of the internal area and surfaces of a tool or tubular assembly through
which there is an unimpeded internal diameter. In some cases, full-bore is used to
describe the form of a nominal internal diameter that extends over the length of the tool
or interval without any variation. In other applications, the term simply implies an ability
to pass a ball or similar item of a stated drift diameter through the assembly.
Gas Cap
The gas cap is the gas that accumulates in the upper portions of a reservoir or tubular
where the pressure, temperature and fluid characteristics are conducive to free gas. The
energy provided by the expansion of the gas cap provides the primary drive mechanism
for oil recovery in such circumstances.
GOR
Abbreviation for gas/oil ratio, the ratio of produced gas to produced oil.
Heavy Oil (Viscous)
Is crude oil with high viscosity and high specific gravity. The API classifies heavy oil as
crudes with a gravity rating below 22.3° API. In addition to high viscosity and high
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specific gravity, heavy oils typically have low hydrogen-to-carbon ratios, high
asphaltene, sulfur, nitrogen, and heavy-metal content, as well as higher acid numbers.
Hot Oiler
A truck- or skid-mounted unit used to heat oil or treatment fluid. Hot oilers are routinely
used in the removal of wax deposits from the upper wellbore section of wells in cold
climates where low wellhead temperatures increase the susceptibility of heavy crude oil
to wax precipitation.
Hot Tapping
Is the process of drilling a hole through a pressure barrier using special equipment and
procedures to ensure that the pressure and fluids are safely contained while the access
port is made. Hot tapping is often used to enable access to the wellbore when wellhead
valves jam closed.
Hot Water Flooding
Is a method of thermal recovery in which hot water is injected into a reservoir through
specially distributed injection wells. Hot water-flooding reduces the viscosity of the crude
oil, allowing it to move more easily toward production wells.
Hot water-flooding, also known as hot water injection, is typically less effective than a
steam-injection process because water has lower heat content than steam. Nevertheless, it
is preferable under certain conditions such as formation sensitivity to fresh water.
H2S (Hydrogen Sulfide)
H2S is an extraordinarily poisonous gas with a molecular formula of H2S. At low
concentrations, H2S has the odor of rotten eggs, but at higher, lethal concentrations, it is
odorless. H2S is hazardous to workers and a few seconds of exposure at relatively low
concentrations can be lethal, but exposure to lower concentrations can also be harmful.
The effect of H2S depends on duration, frequency and intensity of exposure as well as the
susceptibility of the individual.
Hydrogen sulfide is a serious and potentially lethal hazard, so awareness, detection and
monitoring of H2S is essential. Since hydrogen sulfide gas is present in some subsurface
formations, drilling and other operational crews must be prepared to use detection
equipment, personal protective equipment, proper training and contingency procedures in
H2S-prone areas.
Hydrogen sulfide is produced during the decomposition of organic matter and occurs
with hydrocarbons in some areas. It enters drilling mud from subsurface formations and
can also be generated by sulfate-reducing bacteria in stored muds. H2S can cause sulfidestress-corrosion cracking of metals. Because it is corrosive, H2S production may require
costly special production equipment such as stainless steel tubing.
Sulfides can be precipitated harmlessly from water muds or oil muds by treatments with
the proper sulfide scavenger. H2S is a weak acid, donating two hydrogen ions in
neutralization reactions, forming HS- and S-2 ions. In water or water-base muds, the three
sulfide species, H2S and HS- and S-2 ions, are in dynamic equilibrium with water and H+
and OH- ions. The percent distribution among the three sulfide species depends on pH.
H2S is dominant at low pH, the HS- ion is dominant at mid-range pH and S2 ions
dominate at high pH. In this equilibrium situation, sulfide ions revert to H2S if pH falls.
Sulfides in water mud and oil mud can be quantitatively measured with the Garrett Gas
Train according to procedures set by API.
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Hydrates
Hydrates are clathrate compounds (inclusion complexes) formed by the reaction of
molecules of water and another substance such as a hydrocarbon, in which the molecule
of water H—OH bond is not split.
In the oil and gas industry the demand for hydrate removal is significant because hydrates
can block pipelines and Production/Injection wells in an arctic environment. Hydrates can
be removed by depressurization, chemical injection or heating. More specifically
hydrates can be melted by depressurization or injection of coolant, usually MEG
(monoethylene glycol) or methanol, shifting the melting point of the hydrates to below
the ambient temperature, or by installing heating cables or other equipment for heating.
Ice can be removed by the above-mentioned methods as well.
Hydraulic Bypass
Is a design feature on packers and similar down-hole tools that occupy a large proportion
of the drift diameter of the wellbore. When running and retrieving such tools, the
hydraulic bypass allows the wellbore fluid to flow through part of the tool assembly to
reduce the forces applied to the tool and reduce any damaging swab or surge effect on the
reservoir formation.
Hydraulic Packer
A type of packer used predominantly in production applications. A hydraulic packer
typically is set using hydraulic pressure applied through the tubing string rather than
mechanical force applied by manipulating the tubing string.
Hydraulic Packer (Above)
There are several types of packer in common use in oil and gas well completions. In each
case, the principal function is to isolate the annulus from the tubing conduit to enable
controlled production. Setting the packer hydraulically eliminates the need to manipulate
the tubing string, a significant advantage during the well-completion process.
Hydraulic Power Pack
Is an assembly of components and controls necessary to provide a hydraulic power
supply. In modern oilfield activities, many systems are hydraulically powered, including
the majority of mobile systems such as slick-line units, coiled tubing units and snubbing
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units. In most cases, a diesel engine is the prime mover, providing an independent power
supply that is harnessed to the necessary hydraulic pump and control systems.
Hydraulic Release Tool
A down-hole tool designed to allow the lower and upper tool-string sections to be parted
to enable retrieval of the running string. Hydraulic disconnects rely on the application of
a predefined pressure through the running string to activate a release mechanism. In some
cases, a ball or dart is plugged to block circulation through the tool string and enable the
application of the release pressure.
Hydrocarbon
Is a naturally occurring organic compound comprised of Hydrogen and Carbon.
Hydrocarbons can be as simple as methane [CH4], but many are highly complex
molecules, and can occur as gases, liquids or solids. The molecules can have the shape of
chains, branching chains, rings or other structures. Petroleum is a complex mixture of
hydrocarbons. The most common hydrocarbons are natural gas, oil and coal.
Hydrochloric Acid
An acid type commonly used in oil- and gas- well stimulation, especially in carbonate
formations. The reaction characteristics of hydrochloric acid enable it to be used in a
wide range of treatments, often with chemical additives that enhance its performance or
allow greater control of the treatment. Treatments are most commonly conducted with
15% or 28% solutions of hydrochloric acid.
Hydrogen Embrittlement
Is the process whereby steel components become less resistant to breakage and generally
much weaker in tensile strength. While embrittlement has many causes, in the oil field it
is usually the result of exposure to gaseous or liquid hydrogen sulfide [H2S]. On a
molecular level, hydrogen ions work their way between the grain boundaries of the steel,
where hydrogen ions recombine into molecular hydrogen [H2], taking up more space and
weakening the bonds between the grains. The formation of molecular hydrogen can cause
sudden metal failure due to cracking when the metal is subjected to tensile stress.
This type of hydrogen-induced failure is produced when hydrogen atoms enter high
strength steels. The failures due to hydrogen embrittlement normally have a period where
no damage is observed, which is called incubation, followed by a sudden catastrophic
failure.
Hydrogen Sulfide
Is an extraordinarily poisonous gas with a molecular formula of H2S. At low
concentrations, H2S has the odor of rotten eggs, but at higher, lethal concentrations, it is
odorless. H2S is hazardous to workers and a few seconds of exposure at relatively low
concentrations can be lethal, but exposure to lower concentrations can also be harmful.
The effect of H2S depends on duration, frequency and intensity of exposure as well as the
susceptibility of the individual.
Hydrogen sulfide is a serious and potentially lethal hazard, so awareness, detection and
monitoring of H2S is essential. Since hydrogen sulfide gas is present in some subsurface
formations, drilling and other operational crews must be prepared to use detection
equipment, personal protective equipment, proper training and contingency procedures in
H2S-prone areas.
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Hydrogen sulfide is produced during the decomposition of organic matter and occurs
with hydrocarbons in some areas. It enters drilling mud from subsurface formations and
can also be generated by sulfate-reducing bacteria in stored muds. H2S can cause sulfidestress-corrosion cracking of metals. Because it is corrosive, H2S production may require
costly special production equipment such as stainless steel tubing.
Sulfides can be precipitated harmlessly from water or oil mud by treatments with the
proper sulfide scavenger. H2S is a weak acid, donating two hydrogen ions in
neutralization reactions, forming HS- and S-2 ions. In water or water-base mud, the three
sulfide species, H2S and HS- and S-2 ions, are in dynamic equilibrium with water and H+
and OH- ions. The percent distribution among the three sulfide species depends on pH.
H2S is dominant at low pH, the HS- ion is dominant at mid-range pH and S2 ions
dominate at high pH. In this equilibrium situation, sulfide ions revert to H2S if pH falls.
Sulfides in water mud and oil mud can be quantitatively measured with the Garrett Gas
Train according to procedures set by API.
Hydrometer
A weighted, hollow glass bulb with a long, graduated tube attached for measuring the
density of a liquid. A hydrometer is placed in the liquid and the bulb sinks according to
the density of the liquid. Graduations on the tube indicate the density. Hydrometers are
used in fluids that have no gel strength, such as brine, but are not reliable in drilling fluids
because of gelation.
Hydrostatic Bailer
Is a slick-line tool generally used for the removal of sand or similar small particles
around the fishing necks of down-hole tools or equipment. The hydrostatic bailer
incorporates a sealed atmospheric chamber and a shear pin, or similar activation
mechanism, to allow communication with the wellbore. When the tool is activated, there
is a fluid surge into the atmosphere as the pressure is equalized. A shroud arrangement at
the base of the tool contains and directs the fluid surge to dislodge and capture any debris
in the area.
Hydrostatic Pressure (Geological)
Is the normal, predicted pressure for a given depth. Or the pressure exerted per unit area
by a column of fluid from sea level to a given depth.
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Hydrostatic Pressure: The fluid height in columns A and B is identical, but the pressure
reading on the gauges differs because of the different fluid densities. Hydrostatic head
refers to the column height; hydrostatic pressure refers to the force exerted by the fluid.
The Vertical Height of a fluid column, regardless of the length or other dimensions of
that fluid column. For example, a deviated wellbore has a longer length than vertical
depth. The hydrostatic head at any point in that wellbore is not a function of its measured
depth (MD) along the wellbore axis, but rather its vertical distance or true vertical depth
(TVD) to the surface. The term "head" or "hydrostatic head" is also commonly used as a
measure of the output of centrifugal pumps, usually expressed in "feet of head" or psi.
Since this type of pump is a centrifugal (or "velocity") device, the capability of the pump
as expressed in feet of head is independent of the density of the fluid being pumped. For
example, if a pump is rated as producing "sixty feet of head," it will pump a column of
fluid up an open-ended vertical pipe until the top of the liquid is 60 ft [18 m] above the
discharge of the pump, regardless of the density of the liquid being pumped.
Immiscible
Pertaining to phases of fluids or gas that cannot mix to form a homogeneous mixture. Oil
and water are immiscible fluids.
Impermeable
Pertains to a rock that is incapable of transmitting fluids because of low permeability.
Shale has a high porosity, but its pores are small and disconnected, so it is relatively
impermeable. Impermeable rocks are desirable sealing rocks or cap rocks for reservoirs
because hydrocarbons cannot pass through them readily.
Inclination
Is the deviation from vertical, irrespective of compass direction, expressed in degrees.
Inclination is measured initially with a pendulum mechanism, and confirmed with MWD
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accelerometers or gyroscopes. For most vertical wellbores, inclination is the only
measurement of the path of the wellbore. For intentionally deviated wellbores, or wells
close to legal boundaries, directional information is usually also measured.
Inflatable Packer
Is a type of packer that uses an inflatable bladder to expand the packer element against
the casing or wellbore. In preparation for setting the packer, a drop ball or series of tubing
movements are generally required, with the hydraulic pressure required to inflate the
packer provided by carefully applying surface pump pressure. Inflatable packers are
capable of relatively large expansion ratios, an important factor in through-tubing work
where the tubing size or completion components can impose a significant size restriction
on devices designed to set in the casing or liner below the tubing.
Inhibit
To prevent, arrest or slow down any action. For example, one can inhibit a corrosion
process, such as by coating drill-pipe with amine films to arrest pipe corrosion in air. In
drilling fluids, the terms inhibit, inhibition and inhibitive mud system refer to arresting or
slowing the hydration, swelling and disintegration of clays and shale.
Initial Reservoir Pressure
The reservoir pressure measured in a discovery well, usually referred to as pi. This value
is necessary for many reservoir engineering calculations, such as reserve determination.
Initial Shut-in Period
Is the comparatively short shut-in period following the initial flow period for a drill-stem
reservoir test. This period is followed immediately by much longer flow and shut-in
periods to allow the pressure to closely approach initial reservoir pressure. The initial
flow period is commonly 5 to 10 minutes, and the initial shut-in period is commonly 30
minutes to one hour. When plotted on a pressure buildup plot, extrapolation of the best
straight line gives what is usually accepted as the best obtainable value of initial
formation pressure.
Injection Gas
Natural gas injected into a formation to maintain or restore reservoir pressure. Other
reasons for gas injection are gas-lift operations, cycling in gas-condensate reservoirs or
storing gas.
Injection Line
Is a small-diameter conduit that is run alongside production tubulars to enable injection
of inhibitors or similar treatments during production. Conditions such as high hydrogen
sulfide [H2S] concentrations or severe scale deposition can be counteracted by injection
of treatment chemicals and inhibitors during production.
Injection Mandrel
Is a down-hole completion component that enables injection of treatment chemicals or
inhibitors into the production conduit. The injection mandrel is equipped with a port- and
check-valve system to direct fluid pumped down the annulus or injection line into the
production conduit.
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Injection Pressure
The pressure at which a treatment or test fluid can be injected into the formation matrix
without causing a breakdown, or fracture, of the rock matrix. The injection pressure is
commonly described as the surface pump pressure required to achieve injection.
However, since the hydrostatic pressure of the fluid column also contributes to the downhole pressure value, the down-hole pressure should also be considered.
Injection Test (Injectivity)
A procedure conducted to establish the rate and pressure at which fluids can be pumped
into the treatment target without fracturing the formation. Most stimulation treatments
and remedial repairs, such as squeeze cementing, are performed following an injection
test to help determine the key treatment parameters and operating limits.
Injection Well
Is a well in which fluids are injected rather than produced, the primary objective typically
being to maintain reservoir pressure. Two main types of injection are common: gas and
water. Separated gas from production wells or possibly imported gas may be re-injected
into the upper gas section of the reservoir. Water-injection wells are common offshore,
where filtered and treated seawater is injected into a lower water-bearing section of the
reservoir.
Injection Well Testing
Is the testing of wells in which fluid is being injected into the reservoir. The most
common type of test is a falloff test, in which injection is halted and the pressure decline
is measured as a function of time. The most common situation is a water-flood. In many
reservoirs, the formation pressure is high enough to maintain a full column of fluid in the
reservoir, and the pressure can be monitored at the surface. The bottom-hole pressure is
then calculated by adding the weight of the fluid column to the surface pressure. Gasinjection wells, although less common, lend themselves to similar testing. The rise in
fluid pressure as a function of time while injection is taking place could theoretically be
used also, but this type of approach is rarely used. The equations and theory for these
tests are an exact mirror image of those for buildup and drawdown testing. Calculated
results for these wells are usually good because the formations are commonly liquidfilled. Frequently water-injection wells are inadvertently fractured at some time in their
life and consequently have a negative skin effect.
Injector Head
Is one of the principal equipment components of a Coiled Tubing Unit. The injector head
incorporates special profiled chain assemblies to grip the coiled tubing string and a
hydraulic drive system that provides the tractive effort for running and retrieving the
string from the wellbore. The base of the injector head is secured to the wellhead
pressure-control equipment by the stripper assembly mounting system. The gooseneck
mounted on top of the injector head feeds the tubing string from the reel around a
controlled radius into the injector head.
Inside Diameter (ID)
Is the inside or inner diameter. Casing, tubing and drill-pipe are commonly described in
terms of inside diameter and outside diameter (OD).
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Instrument Hanger
Is a down-hole tool on which down-hole gauges or instruments that are to be temporarily
left in the wellbore are attached to. The instrument hanger is run into the wellbore on
slick-line and set in a completion nipple at the required depth.
Instrumented Pig
A device made of rubber or polyurethane that has electronic devices. An instrumented pig
is run through a pipeline to record irregularities that could represent corrosion. An
instrumented pig is also called a smart pig.
Intermittent Gas Lift
Is an artificial-lift method, used in relatively low-productivity wells, in which the gas-lift
system is operated on an intermittent basis to enable the buildup of liquids in the wellbore.
Internal Pulling Tool
A down-hole tool used to pull or retrieve temporary plugs or similar equipment. The
internal pulling tool engages on the internal surfaces of the item to be retrieved.
ISO
Is the abbreviation for the International Organization for Standardization, a developer and
publisher of international standards.
ISO is a network of national-standards institutes from 157 countries, with one member
per country and a Central Secretariat that coordinates the system from offices in Geneva,
Switzerland.
(Recognizing that the acronym for International Organization for Standardization would
vary widely from one member country to the next, ISO founders decided to standardize
the organization acronym. ISO is derived from the Greek isos, meaning equal.)
API and ISO joint committees are developing standards for worldwide use.
Jar (Work-over or well intervention)
A down-hole tool used to deliver an impact force to the tool-string, usually to operate
down-hole tools or to dislodge a stuck tool string. Jars of different designs and operating
principles are commonly included on slick-line, coiled tubing and work-over tool strings.
Simple slick-line jars incorporate an assembly that allows some free travel within the tool
to gain momentum for the impact that occurs at the end of the stroke. Larger, more
complex jars for coiled tubing or work-over strings incorporate a trip or firing mechanism
that prevents the jar from operating until the desired tension is applied to the string, thus
optimizing the impact delivered. Jars are designed to be reset by simple string
manipulation and are capable of repeated operation or firing before being recovered from
the well
(Completions)
Is a down-hole tool that is used to impart a heavy blow or impact load to a down-hole
tool assembly. Commonly used in fishing operations to free stuck objects, jars are
available in a range of sizes and capacities to deliver upward or downward impact loads.
Some slick-line tool assemblies use jars to operate tools that contain shear pins or spring
profiles in their operating method.
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Jet Pump
A type of pump that operates on the principle of a high-pressure fluid jet and the venturi
effect it creates. Jet pumps are relatively inefficient but can tolerate a wide range of
operating conditions, including easily handling sand-laden or abrasive fluids.
Leak Detection
Is the determination of the location of a leak in a pipeline. In onshore operations, this can
be done by external detection or by using material balance leak-detection systems. In
offshore operations, the task is more difficult because of the lack of inlet flow-rate
measurements and the considerable solubility of natural gas in seawater at high pressures
and low temperatures (seafloor level).
In deepwater operations with multiphase flow, indications of a leak may not be present at
the ocean surface or it could be considerably displaced from the site of origination. In
these circumstances, an energy-balance technique based on the changes in frictional
losses through the pipeline is a powerful tool.
Lock
A down-hole device, run and retrieved on slick-line, that is placed and anchored within
the tubing string to provide a setting point for flow-control equipment such as valves,
chokes and plugs. The three main types of lock use different means of locating and
securing: a slip lock locates and anchors anywhere within the correct size of tubing; the
collar lock locates in the space within tubing collars; and the nipple lock locates within
completion nipple profiles.
Lock
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Lock up
A condition that may occur when a coiled tubing string is run into a horizontal or highly
deviated wellbore. Lock-up occurs when the frictional force encountered by the string
running on the wellbore tubular reaches a critical point. Although more tubing may be
injected into the wellbore, the end of the tool string cannot be moved farther into the
wellbore.
Mechanical Jar
A type of jar that incorporates a mechanical trip or firing mechanism that activates only
when the necessary tension or compression has been applied to the running string. In
slick-line operations, the term is often used to describe any jar that does not contain a
hydraulic trip mechanism, such as link and tubular jars that do not incorporate a firing
mechanism.
Naturally Flowing Well
A naturally flowing well in which the formation pressure is sufficient to produce oil at a
commercial rate without requiring a pump. Most reservoirs are initially at pressures high
enough to allow a well to flow naturally.
Oil Formation Volume Factor
Oil and dissolved gas volume at reservoir conditions divided by oil volume at standard
conditions. Since most measurements of oil and gas production are made at the surface,
and since the fluid flow takes place in the formation, volume factors are needed to
convert measured surface volumes to reservoir conditions. Oil formation volume factors
are almost always greater than 1.0 because the oil in the formation usually contains
dissolved gas that comes out of solution in the wellbore with dropping pressure.
Oil Pool
An oil pool is a subsurface oil accumulation. An oil field can consist of one or more oil
pools or distinct reservoirs within a single large trap. The term "pool" can create the
erroneous impression that oil fields are immense caverns filled with oil, instead of rock
filled with small oil-filled pores
Oil Sand
In the context of heavy oil, an oil sand is a porous rock layer, often considered to be a
mixture of sand, clay, water, and bitumen. The term is predominantly used in Canada,
where over 170 billion barrels of bitumen are estimated to be held by large oil sand
deposits in the Athabasca, Cold Lake and Peace River regions of Alberta. Oils from such
sands may have a gravity of less than 10° API. Both in-situ recovery and mining methods
are used to extract the resource, with surface mining used for extracting deposits of extra
heavy oil at shallow depths of less than 100 m [328 ft].
Oil Well
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An oil well is a producing well with oil as its primary commercial product. Oil wells
almost always produce some gas and frequently produce water. Most oil wells eventually
produce mostly gas or water.
Operating Gas Lift Valve
Is the lowermost gas-lift valve in a gas-lift completion through which the lift gas is
injected during normal production. During startup, the upper gas-lift valves open in
sequence, from the top down, to enable the tubing fluids to be displaced. At
predetermined pressures, each of the upper valves closes to eventually route all lift gas
through the operating valve, which is placed at the optimal depth for the reservoir and
completion conditions.
Orifice Meter
Is an instrument that records the flow rate of gas through a pipeline. The flow rate is
calculated from the pressure differential created by the fluid passing through an orifice of
a particular size and other parameters such as static pressure, temperature, density of the
fluid and size of the pipe.
Orifice Valve
An orifice valve is a type of valve (typically found on small-diameter pipe-work) that
incorporates an orifice or flow-restriction device to control fluid flow.
Over-balance
The amount of pressure (or force per unit area) in the wellbore that exceeds the pressure
of fluids in the formation. This excess pressure is needed to prevent reservoir fluids (oil,
gas, water) from entering the wellbore. However, excessive overbalance can dramatically
slow the drilling process by effectively strengthening the near-wellbore rock and limiting
removal of drilled cuttings under the bit. In addition, high overbalance pressures coupled
with poor mud properties can cause differential sticking problems. Because reservoir
pressures vary from one formation to another, while the mud is relatively constant
density, overbalance varies from one zone to another.
Over-Flush
A specially prepared fluid used to displace matrix acid treatments away from the
wellbore at the conclusion of a stimulation treatment. The over-flush is typically
formulated from a weak acid solution or brine to maintain a low pH environment in the
near-wellbore formation that prevents the precipitation of reaction products as the
treatment fluids are flowed back.
The over-flush is normally a weak acid or brine pumped behind the main treating fluid
(mixture of hydrofluoric [HF] and hydrochloric [HCl] or organic acids).
The over-flush has several purposes:
-The displacement of the non-reacted mud acid into the formation.
-The displacement of mud-acid reaction by-products such as amorphous silica. The
minimum over-flush volume should have at least 3 ft [1 m] of radial penetration inside
the formation to displace potential problems away from the critical matrix.
-The removal of potential oil-wet relative-permeability problems caused by some
corrosion inhibitors.
Over Balance
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The amount of pressure (or force per unit area) in the wellbore that exceeds the pressure
of fluids in the formation. This excess pressure is needed to prevent reservoir fluids (oil,
gas, water) from entering the wellbore. However, excessive overbalance can dramatically
slow the drilling process by effectively strengthening the near-wellbore rock and limiting
removal of drilled cuttings under the bit. In addition, high overbalance pressures coupled
with poor mud properties can cause differential sticking problems. Because reservoir
pressures vary from one formation to another, while the mud is relatively constant
density, overbalance varies from one zone to another.
Over-Shot
An over-shot is a down-hole tool used in fishing operations to engage on the outside
surface of a tube or tool. A grapple, or similar slip mechanism, on the overshot grips the
fish, allowing application of tensile force and jarring action. If the fish cannot be
removed, a release system within the overshot allows the overshot to be disengaged and
retrieved.
Paraffin
Paraffin is a hydrocarbon compound that often precipitates on production components as
a result of the changing temperatures and pressures within the production system. Heavy
paraffin occurs as wax-like substances that may build up on the completion components
and may, if severe, restrict production.
Paraffin is normally found in the tubing close to surface in arctic conditions due to the
“permafrost”. Nevertheless, it can form at the perforations, or even inside the formation,
especially in depleted reservoirs or reservoirs under gas-cycling conditions.
Paraffin can be melted or dissolved in most organic solvents, thus, the injection of hot
hydrocarbons is effective for removal of paraffin.
Paraffin Scratcher
A down-hole tool, generally run on slick-line, used to remove paraffin and soft wax
deposits from the internal wall of production tubing and completion equipment.
Perforate
To perforate is to create holes in the casing or liner to achieve efficient communication
between the reservoir and the wellbore. The characteristics and placement of the
communication paths (perforations) can have significant influence on the productivity of
the well. Therefore, a robust design and execution process should be followed to ensure
efficient creation of the appropriate number, size and orientation of perforations. A
perforating gun assembly with the appropriate configuration of shaped explosive charges
and the means to verify or correlate the correct perforating depth can be deployed on
wire-line, tubing or coiled tubing.
Perforate (Over Balance)
To create holes in the liner or casing under conditions in which the hydrostatic pressure
inside the casing or liner is greater than the reservoir pressure. When the perforation is
made, there will be a tendency for the wellbore fluid to flow into the reservoir formation.
Perforate (Under Balance)
To create holes in the liner or casing under conditions in which the hydrostatic pressure
inside the casing or liner is less than the reservoir pressure. When the perforation is made,
there will be a tendency for the reservoir fluid to flow into the wellbore.
Shaped Charge
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Is an explosive device that utilizes a cavity-effect explosive reaction to generate a highpressure, high-velocity jet that creates a perforation tunnel. The shape of the explosive
material and powdered metal lining determine the shape of the jet and performance
characteristics of the charge. The extremely high pressure and velocity of the jet cause
materials, such as steel, cement and rock formations, to flow plastically around the jet
path, thereby creating the perforation tunnel.
Shaped charge: Shaped explosive charges provide an efficient perforation of the optimal
diameter and penetration, while creating minimal debris or formation damage that may
restrict production.
Perforated Interval
The section of wellbore that has been prepared for production by creating channels
between the reservoir formation and the wellbore refers to the “Perforated Interval”. In
many cases, long reservoir sections will be perforated in several intervals, with short
sections of un-perforated casing between each interval to enable isolation devices, like
packers, to be set for subsequent treatments or remedial operations.
Pre-flush
Is a fluid stage, normally hydrochloric acid [HCl], pumped ahead of the main treating
fluid (mixture of hydrofluoric [HF] and hydrochloric [HCl] or organic acids) in a
sandstone matrix-stimulation treatment. One of the purposes of a pre-flush is to displace
formation brines that contain K, Na, Ca ions away from the wellbore, decreasing the
possibility of crystallizing alkali-fluosilicates that could plug the pores. The other purpose
of a pre-flush is to dissolve calcareous materials to minimize calcium fluoride [CaF2]
precipitation, and to dissolve iron scale or rust to avoid the precipitation of the gelatinous,
highly insoluble ferric hydroxide [Fe(OH)3].
Multiple pre-flush stages using brines such as ammonium chloride [NH4Cl] or solvents
are used when multiple damage types are present. A pre-flush is sometimes called a
spearhead.
Pressure Buildup
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A rise in well pressure as a function of time observed after a well is shut in or after the
production rate is reduced. Buildup pressures are normally measured at or near the
bottom of the hole.
Pressure Build-up Analysis
An analysis of data obtained from measurements of the bottom-hole pressure in a well
that is shut-in after a flow period. The profile created on a plot of pressure against time is
used with mathematical reservoir models to assess the extent and characteristics of the
reservoir and the near-wellbore area.
Pressure Depletion
Is the drop in average reservoir pressure from fluid production. All bounded reservoirs
have pressure depletion (a drop in average reservoir pressure) associated with fluid
production. Water influx counters this effect in reservoirs that are surrounded or
underlain by aquifers. Likewise, the presence of a gas cap can slow pressure depletion.
Pressure Drawdown
Is the differential pressure that drives fluids from the reservoir into the well-bore. The
drawdown, and therefore the production rate, of a producing interval is typically
controlled by surface chokes. Reservoir conditions, such as the tendency to produce sand,
may limit the drawdown that may be safely applied during production before damage or
unwanted sand production occurs. It is also a decline in well pressure with time due to
production.
Pressure Drawdown Analysis
The analysis of pressure-transient behavior observed while the well is flowing. Results
are generally much less accurate than those from pressure buildup tests because the
bottom-hole pressure fluctuates rapidly with even slight changes in the surface flow rate.
Therefore, pressure buildup tests are much preferred, and analysis of drawdown test data
is usually relegated to backup status unless the buildup data are flawed.
Pressure Transient Analysis
The analysis of pressure changes over time, especially those associated with small
variations in the volume of fluid. In most well tests, a limited amount of fluid is allowed
to flow from the formation being tested and the pressure at the formation monitored over
time. Then, the well is closed and the pressure monitored while the fluid within the
formation equilibrates. The analysis of these pressure changes can provide information on
the size and shape of the formation as well as its ability to produce fluids.
Pressure Transient Well Tests
Well tests in which pressure is recorded as a function of time and interpreted using
various analysis methods. These include buildup tests and drawdown tests in production
wells and falloff tests in injection wells. Pressure-transient well-test analysis procedures
are based on classical mathematical relationships between flow rate, pressure and time,
which are directly analogous to the theory of heat transfer.
Pressure Fall-off
Is the pressure decline after halting or reducing fluid injection in a well. Pressure falloff
tests in injection wells are analogous to pressure buildup tests in production wells.
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Pressure Gradient
Is a change in pressure as a function of distance. This can refer to radial change in pore
pressure with distance from the well (which can be calculated from well-test analysis
results), to change in pore pressure with depth (which can be measured by formation
tests, and implies formation fluid density and/or fluid contacts) or to change in wellbore
fluid pressure with depth (which can be measured with production logs, and implies
wellbore fluid density).
Radial Differential Temperature Log (Temp Log)
Is an E-line record of the difference in temperature between the opposite sides of the
internal wall of a casing. The log is mainly used to detect a channel in the cement, since
the fluid moving in the channel is likely to be cooler or warmer than its surroundings.
The two temperature probes are held on arms that are extended to touch the casing wall at
depths where a channel is suspected. The assembly is then rotated through 360o to give
the radial differential-temperature log. A sinusoid indicates a channel. Temperature
differences are small, typically 0.005 to 0.05oF [0.003 to 0.03oC], but can be enhanced by
injecting cooler fluids from surface.
Radio Safe Detonator
Electric detonators used in wire-line and electronic firing-head perforating operations,
which are immune to radio interference and thus cannot be accidentally triggered by
radio transmissions.
Radioactive Tracer
Is a component of a production-logging tool that carries a radioactive solution (often
carnotite) that can be selectively released into a flow stream. When the radioactive
solution is released into an injected fluid, the movement of the mixture can be traced by
gamma ray detectors located in the tool.
Radioactive tracers are generally used in injection wells rather than in production wells to
avoid radioactive contamination at the surface. The main applications of radioactive
tracers include establishing flow profiles in injection wells, detecting fluid movements
behind the pipe, and locating leaking packers and fluid movement between wells.
Remedial Cementing
Cementing operations performed to repair primary-cementing problems or to treat
conditions arising after the wellbore has been constructed. The two main categories of
remedial cementing include squeeze cementing and the placement of cement plugs.
Reservoir Communication
Is the flow of fluids from one reservoir to another abutting reservoir or the term is often
used to describe cross-flow from one reservoir compartment to another compartment in
the same reservoir.
Reservoir Pressure
The pressure of fluids within the pores of a reservoir, usually hydrostatic pressure, or the
pressure exerted by a column of water from the formation's depth to sea level. Because
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reservoir pressure changes as fluids are produced from a reservoir, the pressure should be
described as measured at a specific time, such as initial reservoir pressure.
Reservoir Simulation
Is a computer run of a reservoir model over time to examine the flow of fluid within the
reservoir and from the reservoir. Reservoir simulators are built on reservoir models that
include the petrophysical characteristics required to understand the behavior of the fluids
over time. Usually, the simulator is calibrated using historic pressure and production data
in a process referred to as "history matching." Once the simulator has been successfully
calibrated, it is used to predict future reservoir production under a series of potential
scenarios, such as drilling new wells, injecting various fluids or stimulation.
Retrievable Bridge Plug
A type of down-hole isolation tool that may be unset and retrieved from the wellbore
after use, such as may be required following treatment of an isolated zone. A retrievable
bridge plug is frequently used in combination with a packer to enable accurate placement
and injection of stimulation or treatment fluids.
Retrievable Packer
A type of packer that is run and retrieved on a running string or production string, unlike
a permanent production packer that is set in the casing or liner before the production
string is run. Retrievable packers are most commonly used in well intervention activities,
although some completion designs are more suited to retrievable packers than permanent
packers.
Reverse Circulation
To circulate fluid down the wellbore annulus, with returns being made up the tubing
string. Reverse circulation often is used to remove debris from the wellbore since the
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high fluid flow rate inside the tubing string enables the recovery of large or dense debris
particles that are difficult or impossible to remove with conventional circulation.
Reverse Circulating Valve
A down-hole tool that is designed to enable communication between the tubing internal
diameter and the annulus, typically for reverse circulation purposes, although
conventional circulation often can also be undertaken. The valve design may be simple,
enabling circulation without the ability to reset the tool until it is retrieved to surface, or
be of a more complex design allowing several cycles between open and closed positions.
Roller Stem
A down-hole tool used on slick-line operations conducted on a deviated wellbore to
provide additional mass to the tool string. Incorporated in the assembly, rollers reduce the
friction encountered as the roller stem is run along the wellbore. This, together with the
additional mass, helps achieve deeper slick-line penetration of deviated wellbores.
Rotational Gas Lift
Is a gas-lift system that recycles the injected gas using compressors. This closed system
does not require an external source of gas for operating the gas-lift system.
Running Tool
A generic name for a tool or device that is used in the placement or setting of down-hole
equipment such as permanent packers or plugs. The running tool can be retrieved after
the operation or setting process. In some cases, the running tool also is used to retrieve
the equipment or tool that has been set in the wellbore.
A down-hole tool used to run and set down-hole plugs or similar equipment. The term
applies to a range of tools used in work-over activities, such as coiled tubing, snubbing or
rig-based applications. However, the term is most commonly associated with slick-line
operations, referring to the tools used to run and set slick-line locks, plugs and similar
down-hole equipment.
Sand Bailer
A down-hole device, usually run on slick-line, used to remove sand or debris from the
bottom of the wellbore. In operation, an atmospheric chamber within the tool is opened to
create a surge of fluids into the chamber. Debris is then held within the chamber for
recovery at surface.
A swabbing device used to clean up sand that has accumulated in the wellbore. Because
sand’s abrasiveness is detrimental to the normal operation of production equipment, its
production should be minimized. A sand bailer operates by creating a partial vacuum that
sucks up the sand.
Sand Cleanout
The process of removing sand or similar fill from a wellbore. Many wells produce sand
that may accumulate and restrict production if not removed from the wellbore by the
production fluid. Coiled tubing and snubbing units are routinely used for sand-cleanout
operations, enabling the well condition to be treated without removing the completion
equipment or even killing the well.
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Sanded Off
A condition encountered during some hydraulic fracturing operations whereby the
fracture cannot accept further sand or proppant and only the carrier fluid is injected into
the formation. A “Sand Off” occurs when the concentration of proppant within the tubing
string rapidly increases, creating a corresponding sudden increase in pump pressure.
Scale
A mineral salt deposit that may occur on wellbore tubing and components as the
saturation of produced water is affected by changing temperature and pressure conditions
in the production conduit. In severe conditions, scale creates a significant restriction, or
even a plug, in the production tubing. Scale removal is a common well-intervention
operation, with a wide range of mechanical, chemical and scale inhibitor treatment
options available.
Also: A mineral salt deposit that may occur on wellbore tubing and components as the
saturation of produced water is affected by changing temperature and pressure conditions
in the production conduit. In severe conditions, scale creates a significant restriction, or
even a plug, in the production tubing. Scale removal is a common well-intervention
operation, with a wide range of mechanical, chemical and scale inhibitor treatment
options available.
Scale Inhibitor
A chemical treatment used to control or prevent scale deposition in the production
conduit or completion system. Scale-inhibitor chemicals may be continuously injected
through a down-hole injection point in the completion, or periodic squeeze treatments
may be undertaken to place the inhibitor in the reservoir matrix for subsequent
commingling with produced fluids.
Some scale-inhibitor systems integrate scale inhibitors and fracture treatments into one
step, which guarantees that the entire well is treated with scale inhibitor. In this type of
treatment, a high-efficiency scale inhibitor is pumped into the matrix surrounding the
fracture face during leak-off. It adsorbs to the matrix during pumping until the fracture
begins to produce water. As water passes through the inhibitor-adsorbed zone, it
dissolves sufficient inhibitor to prevent scale deposition. The inhibitor is better placed
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than in a conventional scale-inhibitor squeeze, which reduces the retreatment cost and
improves production.
Scale Inhibitor Squeeze
A type of inhibition treatment used to control or prevent scale deposition. In a scaleinhibitor squeeze, the inhibitor is pumped into a water-producing zone. The inhibitor is
attached to the formation matrix by chemical adsorption or by temperature-activated
precipitation and returns with the produced fluid at sufficiently high concentrations to
avoid scale precipitation. Some chemicals used in scale-inhibitor squeezes are
phosphonated carboxylic acids or polymers.
Scale Removal
A common well-intervention operation involving a wide variety of mechanical scaleinhibitor treatments and chemical options. Mechanical removal is done by means of a pig
or by abrasive jetting that cuts scale but leaves the tubing untouched. Scale-inhibition
treatments involve squeezing a chemical inhibitor into a water-producing zone for
subsequent commingling with produced fluids, preventing further scale precipitation.
Chemical removal is performed with different solvents according to the type of scale:
- Carbonate scales such as calcium carbonate or calcite [CaCO3] can be readily dissolved
with hydrochloric acid [HCl] at temperatures less than 250oF [121oC].
- Sulfate scales such as gypsum [CaSO4·2H2O] or anhydrite [CaSO4] can be readily
dissolved using ethylenediamine tetraacetic acid (EDTA). The dissolution of barytine
[BaSO4] or strontianite [SrSO4] is much more difficult.
- Chloride scales such as sodium chloride [NaCl] are easily dissolved with fresh water or
weak acidic solutions, including HCl or acetic acid.
- Iron scales such as iron sulfide [FeS] or iron oxide [Fe2O3] can be dissolved using HCl
with sequestering or reducing agents to avoid precipitation of by-products, for example
iron hydroxides and elemental sulfur.
Seal Bore Packer
A type of production packer that incorporates a seal-bore that accepts a seal assembly
fitted to the bottom of the production tubing. The seal-bore packer is often set on wireline to enable accurate depth correlation. For applications in which a large tubing
movement is anticipated, as may be due to thermal expansion, the seal-bore packer and
seal assembly function as a slip joint.
Shear Pin
A short piece of brass or steel that is used to retain sliding components in a fixed position
until sufficient force is applied to break the pin. Once the pin is sheared, the components
can then move to operate or function the tool.
Shifting Tool
A down-hole tool, most commonly associated with slick-line operations that is used to
open, close or shift the position of down-hole flow control or circulation devices, such as
sliding sleeves. The shifting tool generally features some means of engaging the
components to be shifted and is typically run with upward or downward operating jars to
deliver the necessary force or impact.
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Also: A down-hole tool used to adjust the position of sliding sleeves or similar
production and completion equipment. Shifting tools are typically run on slick-line,
although they may be used with coiled tubing in deviated or horizontal wellbores.
Shifting tools are generally prepared or dressed for use with a specific model and size of
sliding sleeve, requiring careful selection of the appropriate shifting tool.
Shoot a Level
To use a special acoustic device to determine the fluid level in a conduit or annular space.
The principle of operation relies on accurately recording the time taken for a return echo
to be bounced from the fluid in contained area.
Shut-in Bottom Hole Pressure
The force per unit area exerted at the bottom of a wellbore when it is closed at either the
Christmas tree or the BOP stack. The SIBP is generated by a combination of the
hydrostatic pressure from the weight of the liquid in the well and any additional applied
pressure. The applied pressure component may be from the formation or from an external
source at the surface.
Shut-in Well (Statics)
A well with a valve closed to halt production. Wells are often shut-in for a period of time
for any number of reasons. One for instance; to allow stabilization prior to beginning a
drawdown-buildup test sequence. They should also have been freeze protected (pickled)
to keep the upper tubing/casing from icing up in the permafrost layer that ranges
anywhere from a 2000’ depth to surface in the north slope Alaska oil fields.
Side Pocket Mandrel
A completion component that is used to house gas-lift valves and similar devices that
require communication with the tubing and the annulus. The design of a side-pocket
mandrel is such that the installed components do not obstruct the production flow path,
enabling access to the wellbore and completion components below.
Static Fluid Level
Is the level to which fluid rises in a well when the well is shut in. The hydrostatic head of
this fluid is equal to the well bottom-hole pressure.
Tag
To contact, or tag, a known reference point or obstruction in the wellbore with the tubing
string, wire-line or other intervention equipment.
Tail Pipe
The tubulars and completion components run below a production packer. The tail pipe
may be included in a completion design for several reasons. It can provide a facility for
plugs and other temporary flow-control devices, improve down-hole hydraulic
characteristics, and provide a suspension point for down-hole gauges and monitoring
equipment.
Temperature Log
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Is a record of the temperature gradient in a well. The temperature log is interpreted by
looking for anomalies, or departures, from the reference gradient. This reference might be
the geothermal gradient, a log recorded before production started or a log recorded with
the well shut-in. Most anomalies are related to the entry of fluids into the borehole or
fluid exit into the formation. Since the temperature is affected by material outside the
casing, a temperature log is sensitive to not only the borehole but also the formation and
the casing-formation annulus.
Temperature logs have many applications, with the most common being to identify zones
producing or taking fluid, to evaluate a cement or hydraulic fracture treatment, and to
locate lost circulation zones and casing leaks. Since temperature takes time to dissipate, a
temperature log tends to reflect the behavior of a well over a longer time period than
other measurements.
Temperature Survey
Is a temperature data set taken at various depths in the well-bore. Temperature surveys
are used to determine the top of cement behind the casing, fluid contacts and water
influx. It is also useful to check for valve and casing leaks after the well has been
temporarily shut down.
Thermal Gradient
Is the rate of increase in temperature per unit depth in the Earth’s mass. Although the
thermal gradient varies from place to place, it averages 25 to 30oC/km [15 oF/1000 ft].
Threshold Velocity (Turbine Meter or E-line Spinner)
In a spinner flow-meter, the theoretical minimum fluid velocity required to initiate
spinner rotation, assuming the spinner response is linear. The actual fluid velocity
required to start spinner rotation is slightly higher because of additional viscous and
mechanical effects. The threshold velocity is determined by extrapolating the spinner
response at higher fluid velocities, where it is known to be nearly linear, back to the value
that exists when spinner rotation is zero.
Tight Hole
Describing a relatively impermeable reservoir rock from which hydrocarbon production
is difficult. Stimulation of tight formations can result in increased production from
formations that previously would have been abandoned or produced uneconomically.
Total Depth
The planned end of the well, measured by the length of pipe required to reach the bottom.
True Vertical Depth
Is the vertical distance from a point in the well (usually the current or final depth) to a
point at the surface, usually the elevation of the rotary Kelly bushing (RKB). This is one
of two primary depth measurements used by the drillers, the other being measured depth.
TVD is important in determining bottom-hole pressures, which are caused in part by the
hydrostatic head of fluid in the wellbore. For this calculation, measured depth is
irrelevant and TVD must be used. For most other operations, the driller is interested in
the length of the hole or how much pipe will fit into the hole. For those measurements,
measured depth, not TVD, is used. While the drilling crew should be careful to designate
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which measurement they are referring to, if no designation is used, they are usually
referring to measured depth. Note that measured depth, due to intentional or unintentional
curves in the wellbore, is always longer than true vertical depth.
True vertical depth. The true vertical depth is the vertical depth of the wellbore
independent of its path. In the case of a vertical well, measured depth is the same as true
vertical depth. This illustration demonstrates, however, that a deviated wellbore has a
longer measured depth than true vertical depth.
Transition Flow
Is a multiphase-fluid flow regime characterized by a chaotic mixture of liquid and gas,
with neither phase appearing to be continuous. Also known as churn flow, transition flow
is an intermediate flow condition between slug flow and mist flow.
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The relative behavior of fluid phases is summarized in four basic flow regimes. Although
more than one flow regime may occur because of changing conditions throughout the
wellbore, the efficient transport of liquid from the wellbore relies on sufficient energy
being available.
Tubing Broach
A down-hole tool used to repair damaged or collapsed tubing. The tubing broach
incorporates a cutter profile that is forced inside the tubing by jarring or hydraulic force
to re-form the tubing wall by removing tubing wall material and forcing the tubing wall
into place.
Tubing End Locator
A down-hole tool frequently used in slick-line or coiled tubing tool assemblies to confirm
or correlate the tool position on depth-sensitive applications. With the end of the
production tubing as a known reference point, any error in measurement that may occur
in reaching the treatment depth will be significantly less than what may have resulted if
measuring from surface.
Tubing Pressure
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Is pressure on the tubing in a well, as measured at the well-head.
Tubing Retrievable Safety Valve (SSSV)
Is a type of subsurface safety valve that is run and retrieved as part of the production
tubing string. The TRSV body is integral part of the completion that enables the internal
components to be configured to provide near full-bore access through the valve. An
external control line is secured to the running string for connection to a surface-control
system.
U-tube Effect
In a U-tube manometer, the height of one leg of fluid changed by altering the density of
some of the fluid in the other leg. In a well with drill-pipe in the hole, the string of drillpipe is one leg and the annulus between the drill-pipe and the wellbore is the other. If a
denser mud goes into the drill-pipe, mud flows up the annulus, and vice versa. The
practice of putting a dense slugging pill in the drill-pipe in order to pull a dry string
makes use of the U-tube effect.
Under Balance
The amount of pressure (or force per unit area) exerted on a formation exposed in a
wellbore below the internal fluid pressure of that formation. If sufficient porosity and
permeability exist, formation fluids enter the wellbore. The drilling rate typically
increases as an underbalanced condition is approached.
Unload
To initiate flow from a reservoir by removing the column of kill fluid from the wellbore.
Several methods of unloading the well are used, including circulation of lower density
fluid, nitrogen lifting and swabbing. The method used will depend on the completion
design, reservoir characteristics and local availability.
Vapor Extraction
A non-thermal heavy oil production method. Similar in concept to SAGD, in vapor
extraction a solvent vapor is used to reduce viscosity of the heavy oil. The injected
solvent vapor expands and dilutes the heavy oil by contact. The diluted heavy oil will
drain by gravity to the lower horizontal well, to be produced.
Vapor Pressure
The pressure exerted by a vapor escaping from a liquid. It quantifies the tendency of
molecules to enter the gaseous phase. The vapor pressure of water increases as
temperature increases and reaches one atmosphere pressure (760 mm Hg or 14.7 psia) at
the boiling point (100°C or 212°F). The activity of an aqueous solution is the ratio of
vapor pressures: aw = p/po, where p = vapor pressure of a solution and po is vapor
pressure of pure water. Since this is a ratio of vapor pressures, activity is not a strong
function of temperature.
Vertical Lift
The vertical distance between two points in a horizontal or deviated wellbore. Any
calculations relating to wellbore pressure or down-hole pump performance will be based
on the vertical lift rather than the distance traveled through the wellbore.
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WAG (Water Alternating Gas)
An enhanced oil recovery process whereby water injection and gas injection are
alternately injected for periods of time to provide better sweep efficiency and reduce gas
channeling from injector to producer. This process is used mostly in CO2 floods to
improve hydrocarbon contact time and sweep efficiency of the CO.
Wall Loss
The loss of material on the inside or outside of a casing or tubing due to corrosion.
Monitoring wall loss in situ helps determine when the pipe may be at risk for leaking or
failure. Wall loss is determined by comparing casing or tubing thickness measured by
electromagnetic, acoustic resonance or mechanical methods with either an earlier
measurement or an assumed value.
Water Cut
The ratio of water produced compared to the volume of total liquids produced. The water
cut in water-drive reservoirs can reach very high values.
Water-flood
A method of secondary recovery in which water is injected into the reservoir formation to
displace residual oil. The water from injection wells physically sweeps the displaced oil
to adjacent production wells. Potential problems associated with water-flood techniques
include inefficient recovery due to variable permeability, or similar conditions affecting
fluid transport within the reservoir, and early water breakthrough that may cause
production and surface processing problems.
Water Injection
Water injected into the reservoir to pressurize and displace hydrocarbons to producing
wells. Injection water is also used in water-storage operations in offshore and remote
locations with economic and environmental constraints.
Wellbore Diagram
A schematic diagram that identifies the main completion components installed in a
wellbore. The information included in the wellbore diagram relates to the principal
dimensions of the components and the depth at which the components are located. A
current wellbore diagram should be available for any well intervention operation to
enable engineers and equipment operators to select the most appropriate equipment and
prepare operating procedures that are compatible with any down-hole restrictions.
Wire-line Cut Bar
A down-hole tool used to cut slick-line from a tool string that is stuck or jammed in a
wellbore. The wire-line cutter is attached to the slick-line at surface and dropped down
the wellbore. When the cutting tool impacts the tool string, a cutting mechanism cuts the
slick-line and enables recovery of the line in preparation for further fishing operations.
Wire Clamp
A safety device attached to the slick-line at surface between the hay pulley and stuffingbox pulley. The wire clamp generally is applied when the slick-line is to be stationary for
a period of time. This prevents the tool string from dropping down the wellbore if the
winch unit fails or the slick-line becomes damaged at surface.
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Wire Grab
A fishing tool used for the retrieval of broken or cut slick-line from the wellbore. Wireline grabs are intended to catch and engage wire-line that has been bunched or nested in
the wellbore. For that reason, they are often run after a blind box or similar full-bore tool
has been used to nest the wire-line.
Wire-line Retrievable Safety Valve (WRSV)
A type of safety valve in which the principal components can be run and retrieved by
wireline or slickline. The valve assembly is landed in a ported nipple that is equipped
with a control line connected to the surface control system. This configuration enables the
safety valve to be easily retrieved for repair or maintenance, but the resulting internal
bore of the WRSV must be relatively small.
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Drilling Rigs
Blowout Preventer
A large valve at the top of a well that may be closed if the drilling crew loses control of
formation fluids. By closing this valve (usually operated remotely via hydraulic
actuators), the drilling crew usually regains control of the reservoir, and procedures can
then be initiated to increase the mud density until it is possible to open the BOP and
retain pressure control of the formation. BOPs come in a variety of styles, sizes and
pressure ratings. Some can effectively close over an open wellbore, some are designed to
seal around tubular components in the well (drill-pipe, casing or tubing) and others are
fitted with hardened steel shearing surfaces that can actually cut through drill-pipe. Since
BOPs are critically important to the safety of the crew, the rig and the wellbore itself,
BOPs are inspected, tested and refurbished at regular intervals determined by a
combination of risk assessment, local practice, well type and legal requirements. BOP
tests vary from daily function testing on critical wells to monthly or less frequent testing
on wells thought to have low probability of well control problems.
Blowout preventer. This BOP configuration is typical for a well drilled with a hole size
greater than 4-in. diameter.
Casing
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Drilling
Large-diameter pipe lowered into an open-hole and cemented in place. The well designer
must design casing to withstand a variety of forces, such as collapse, burst, and tensile
failure, as well as chemically aggressive brines. Most casing joints are fabricated with
male threads on each end, and short-length casing couplings with female threads are used
to join the individual joints of casing together, or joints of casing may be fabricated with
male threads on one end and female threads on the other. Casing is run to protect fresh
water formations, isolate a zone of lost returns or isolate formations with significantly
different pressure gradients. The operation during which the casing is put into the
wellbore is commonly called "running pipe." Casing is usually manufactured from plain
carbon steel that is heat-treated to varying strengths, but may be specially fabricated of
stainless steel, aluminum, titanium, fiberglass and other materials.
Well Completions
Steel pipe cemented in place during the construction process to stabilize the wellbore.
The casing forms a major structural component of the wellbore and serves several
important functions: preventing the formation wall from caving into the wellbore,
isolating the different formations to prevent the flow or cross-flow of formation fluid, and
providing a means of maintaining control of formation fluids and pressure as the well is
drilled. The casing string provides a means of securing surface pressure control
equipment and down-hole production equipment, such as the drilling blowout preventer
(BOP) or production packer. Casing is available in a range of sizes and material grades.
Conductor Pipe
The casing string that is usually put into the well first, particularly on land wells, to
prevent the sides of the hole from caving into the wellbore. This casing, sometimes called
drive pipe, is generally a short length and is sometimes driven into the ground. Conductor
pipe is run because the shallow section of most wells onshore is drilled in unconsolidated
sediment or soil rather than consolidated strata typically encountered deeper. Offshore,
the drive pipe or structural casing may be installed prior to the conductor for similar
reasons.
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Casing. The casing strings used in the design and construction of a wellbore can be
configured in a range of sizes and depths, mainly determined by the formation
characteristics and local availability. The wellbore configuration shown is commonly
found in conventional vertical wells, with the casing setting depth for each string
determined by the specific formation or reservoir conditions
Casing Hanger
The subassembly of a wellhead that supports the casing string when it is run into the
wellbore. The casing hanger provides a means of ensuring that the string is correctly
located and generally incorporates a sealing device or system to isolate the casing
annulus from upper wellhead components.
Casing hanger. Attached to the topmost joint of casing, the casing hanger incorporates
features to suspend the casing string and provide hydraulic isolation once engaged in the
casing bowl.
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Casing Shoe
The bottom of the casing string (including the cement around it), or the equipment run at
the bottom of the casing string.
A short assembly, typically manufactured from a heavy steel collar and profiled cement
interior, that is screwed to the bottom of a casing string. The rounded profile helps guide
the casing string past any ledges or obstructions that would prevent the string from being
correctly located in the wellbore.
Casing shoe: The external profile of the casing shoe helps guide the casing string into the
wellbore.
Cement Shoe and Float
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Casing shoe. The external profile of the casing shoe helps guide the casing string into the
wellbore.
Cat Line
A relatively thin cable used with other equipment to move small rig and drill-string
components and to provide tension on the tongs for tightening or loosening threaded
connections.
Company Man
Is the representative of the oil company (or operator) on a drilling location. For land
operations, the company man is responsible for operational issues on the location,
including the safety and efficiency of the project. Even administrative managers are
expected to respond to the direction of the company man when they are on the rig-site.
Offshore, depending on the regulatory requirements, there may be an offshore installation
manager, who supervises the company man on safety and vessel integrity issues, but not
on operational issues.
Crown Block
The fixed set of pulleys (called sheaves) located at the top of the derrick or mast, over
which the drilling line is threaded. The companion blocks to these pulleys are the
traveling blocks. By using two sets of blocks in this fashion, great mechanical advantage
is gained, enabling the use of relatively small drilling line (3/4 to 1 1/2 in. diameter steel
cable) to hoist loads many times heavier than the cable could support as a single strand.
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Crown Block. The pulleys that make up the crown block allow the cable to hoist heavy
loads.
Cuttings
Cuttings are small pieces of rock that break away due to the action of the bit teeth.
Cuttings are screened out of the liquid mud system at the shale shakers and are monitored
for composition, size, shape, color, texture, hydrocarbon content and other properties by
the mud engineer, the mud logger and other on-site personnel. The mud logger usually
captures samples of cuttings for subsequent analysis and archiving.
Derrick
The structure used to support the crown blocks and the drill-string of a drilling rig.
Derricks are usually pyramidal in shape, and offer a good strength-to-weight ratio. If the
derrick design does not allow it to be moved easily in one piece, special ironworkers must
assemble them piece by piece, and in some cases disassemble them if they are to be
moved.
Derrick-man
One of the rig crew members who gets his name from the fact that he works on a
platform attached to the derrick or mast, typically 85 ft [26 m] above the rig floor, during
trips. On small land drilling crews, the derrick-man is second in rank to the driller. Larger
offshore crews may have an assistant driller between the derrick-man and the driller. In a
typical trip out of the hole (TOH), the derrick-man wears a special safety harness that
enables him to lean out from the work platform (called the monkey-board) to reach the
drill-pipe in the center of the derrick or mast, throw a line around the pipe and pull it back
into its storage location (the fingerboards) until it is time to run the pipe back into the
well. In terms of skill, physical exertion and perceived danger, a derrick-man has one of
the most demanding jobs on the rig crew. Some modern drilling rigs have automated
pipe-handling equipment such that the derrick-man controls the machinery rather than
physically handling the pipe. In an emergency, the derrick-man can quickly reach the
ground by an escape line often called the Geronimo line.
Diamond Bit
A tool for drilling rock that works by scraping industrial grade diamonds against the
bottom of the hole. The diamonds are embedded into the metal structure (usually a
sintered or powdered carbide base matrix) during the manufacture of the bit. The bit
designer has virtually unlimited combinations of bit shape, the placement of hydraulic
jetting ports, the amount of diamonds and the size of the diamonds used (usually
expressed as diamonds per carat). In general, a diamond bit that drills faster has a shorter
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lifetime. Similarly, a bit designed for extremely long life will typically drill at a slower
rate. If a bit has a relatively high number of diamonds compared with other bits, it is said
to be "heavy-set" and has higher durability. A "light-set" bit, on the other hand, drills
more aggressively, but wears out faster because fewer diamonds do the work.
Directional Driller
An individual trained in the science and art of intentionally drilling a well along a
predetermined path in three-dimensional space, usually involving deviating the well from
vertical and directing it in a specific compass direction or heading. The directional driller
considers such parameters as rotary speed, weight on bit, control drilling and when to
stop drilling and take surveys of the well-path, and works closely with the tool-pusher.
Directional Drilling
The intentional deviation of a wellbore from the path it would naturally take. This is
accomplished through the use of whip-stocks, bottom-hole assembly (BHA)
configurations, instruments to measure the path of the wellbore in three-dimensional
space, data links to communicate measurements taken down-hole to the surface, mud
motors and special BHA components and drill bits. The directional driller also exploits
drilling parameters such as weight on bit and rotary speed to deflect the bit away from the
axis of the existing wellbore. In some cases, such as drilling steeply dipping formations
or unpredictable deviation in conventional drilling operations, directional-drilling
techniques may be employed to ensure that the hole is drilled vertically. While many
techniques can accomplish this, the general concept is simple: point the bit in the
direction that one wants to drill. The most common way is through the use of a bend near
the bit in a down-hole steerable mud motor. The bend points the bit in a direction
different from the axis of the wellbore when the entire drill-string is not rotating. By
pumping mud through the mud motor, the bit turns while the drill-string does not rotate,
allowing the bit to drill in the direction it points. When a particular wellbore direction is
achieved, that direction may be maintained by rotating the entire drill-string (including
the bent section) so that the bit does not drill in a single direction off the wellbore axis,
but instead sweeps around and its net direction coincides with the existing wellbore.
Rotary steerable tools allow steering while rotating, usually with higher rates of
penetration and ultimately smoother boreholes.
Directional Well
Is a wellbore that requires the use of special tools or techniques to ensure that the
wellbore path hits a particular subsurface target, typically located away from (as opposed
to directly under) the surface location of the well.
Displacement
Dog-house
The Dog-house is a steel-sided room adjacent to the rig floor, usually having an access
door close to the driller's controls. This general-purpose shelter is a combination tool
shed, office, communications center, coffee room, lunchroom and general meeting place
for the driller and his crew. It is at the same elevation as the rig floor, usually cantilevered
out from the main substructure supporting the rig.
Draw Works
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Is a machine on the rig consisting of a large-diameter steel spool, brakes, a power source
and assorted auxiliary devices. The primary function of the draw-works is to reel out and
reel in the drilling line, a large diameter wire rope, in a controlled fashion. The drilling
line is reeled over the crown block and traveling block to gain mechanical advantage in a
"block and tackle" or "pulley" fashion. This reeling out and in of the drilling line causes
the traveling block, and whatever may be hanging underneath it, to be lowered into or
raised out of the wellbore. The reeling out of the drilling line is powered by gravity and
reeling in by an electric motor or diesel engine.
The draw-works reel the drilling line in or out over the crown blocks to raise or lower the
traveling block. This photograph shows the spool-like draw-works without the drilling
line.
Driller
The Driller is the supervisor of the rig crew. The driller is responsible for the efficient
operation of the rig-site as well as the safety of the crew and typically has many years of
rig-site experience. Most drillers have worked their way up from other rig-site jobs.
While the driller must know how to perform each of the jobs on the rig, his or her role is
to supervise the work and control the major rig systems. The driller operates the pumps,
draw-works, and rotary table via the drillers console-a control room of gauges, control
levers, rheostats, and other pneumatic, hydraulic and electronic instrumentation. The
driller also operates the draw-works brake using a long-handled lever. Hence, the driller
is sometimes referred to as the person who is "on the brake."
Drilling Crew
Personnel who operate the drilling rig. The crew typically consists of roustabouts,
roughnecks, floor hands, lead tong operators, motormen, derrick-men, assistant drillers,
and the driller. Since drilling rigs operate around the clock, there are at least two crews
(twelve hour work shifts called tours).
Drilling Fluid
Is any of a number of liquid and gaseous fluids and mixtures of fluids and solids (as solid
suspensions, mixtures and emulsions of liquids, gases and solids) used in operations to
drill boreholes into the earth. They are synonymous with "drilling mud" in general usage,
although some prefer to reserve the term "drilling fluid" for more sophisticated and welldefined "muds." The classifications of drilling fluids has been attempted in many ways,
often producing more confusion than insight. One classification scheme, given here, is
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based only on the mud composition by singling out the component that clearly defines the
function and performance of the fluid: (1) water-base, (2) non-water-base and (3) gaseous
(pneumatic). Each category has a variety of subcategories that overlap each other
considerably.
Escape Line
A steel cable attached to the rig derrick or mast near the work platform for the derrickman. This cable is anchored at surface level (on a vessel or the Earth) away from the mast
in a loose catenary profile, and fitted with a handle and hand brake that is stored at the
top. The escape line provides a rapid escape path for the derrick-man should well
conditions or massive mechanical failure warrant. In such a case the derrick-man would
disconnect his safety belt from the rig, re-hook it over the escape line if time permitted,
firmly grip the tee-bar handle and ride the trolley down the cable while holding on to the
handle with his hands. The escape line is also known as the "Geronimo line."
Horizontal Drilling
A subset of the more general term "directional drilling," used where the departure of the
wellbore from vertical exceeds about 80 degrees. Note that some horizontal wells are
designed such that after reaching true 90-degree horizontal, the wellbore may actually
start drilling upward. In such cases, the angle past 90 degrees is continued, as in 95
degrees, rather than reporting it as deviation from vertical, which would then be 85
degrees. Because a horizontal well typically penetrates a greater length of the reservoir, it
can offer significant production improvement over a vertical well.
Inside Blowout Preventer
Is a valve in the drill-string that may be used to prevent the well from flowing
uncontrollably up the drill-string.
Intermediate Casing
Is the casing string that is generally set in place after the surface casing and before the
production casing. The intermediate casing string provides protection against caving of
weak or abnormally pressured formations and enables the use of drilling fluids of
different density necessary for the control of lower formations.
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Jar (Drilling)
A mechanical device used down-hole to deliver an impact load to another down-hole
component, especially when that component is stuck. There are two primary types,
hydraulic and mechanical jars. While their respective designs are quite different, their
operation is similar. Energy is stored in the drill-string and suddenly released by the jar
when it fires. The principle is similar to that of a carpenter using a hammer. Kinetic
energy is stored in the hammer as it is swung, and suddenly released to the nail and board
when the hammer strikes the nail. Jars can be designed to strike up, down, or both. In the
case of jarring up above a stuck bottom-hole assembly, the driller slowly pulls up on the
drill-string but the BHA does not move. Since the top of the drill-string is moving up, this
means that the drill-string itself is stretching and storing energy. When the jars reach their
firing point, they suddenly allow one section of the jar to move axially relative to a
second, being pulled up rapidly in much the same way that one end of a stretched spring
moves when released. After a few inches of movement, this moving section slams into a
steel shoulder, imparting an impact load. In addition to the mechanical and hydraulic
versions, jars are classified as drilling jars or fishing jars. The operation of the two types
is similar, and both deliver approximately the same impact blow, but the drilling jar is
built such that it can better withstand the rotary and vibrational loading associated with
drilling.
Jar. This hydraulic jar can be used to free stuck down-hole components.
Joint
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A joint is considered a length of pipe, usually referring to drill-pipe, casing or tubing.
While there are different standard lengths, the most common drill-pipe joint length is
around 30 ft. For casing, the most common length of a joint is 40 ft.
Junk
Anything in the wellbore that is not supposed to be there. The term is usually reserved for
small pieces of steel such as hand tools, small parts, bit nozzles, pieces of bits or other
down-hole tools, and remnants of milling operations.
Kelly
A long square or hexagonal steel bar with a hole drilled through the middle for a fluid
path. The Kelly is used to transmit rotary motion from the rotary table or Kelly bushing
to the drill-string, while allowing the drill-string to be lowered or raised during rotation.
The Kelly goes through the Kelly bushing, which is driven by the rotary table. The Kelly
bushing has an inside profile matching the Kelly's outside profile (either square or
hexagonal), but with slightly larger dimensions so that the Kelly can freely move up and
down inside.
Diagram of Kelly
Kelly Bushing
Is an adapter that serves to connect the rotary table to the Kelly. The Kelly bushing has an
inside diameter profile that matches that of the Kelly, usually square or hexagonal. It is
connected to the rotary table by four large steel pins that fit into mating holes in the
rotary table. The rotary motion from the rotary table is transmitted to the bushing through
the pins, and then to the Kelly itself through the square or hexagonal flat surfaces
between the Kelly and the Kelly bushing. The Kelly then turns the entire drill-string
because it is screwed into the top of the drill-string itself. Depth measurements are
commonly referenced to the KB, such as 8327 ft KB, meaning 8327 feet below the Kelly
bushing.
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)
Photograph of Kelly bushing
Kelly Down
Referring to the condition that occurs when the Kelly is all the way down, so drilling
progress cannot continue. A connection must be made, which has the effect of raising the
Kelly up by the length of the new joint of drill-pipe added, so drilling can resume.
Kelly Hose
Is the large-diameter (3- to 5-in. inside diameter), high-pressure flexible line used to
connect the standpipe to the swivel. This flexible piping arrangement permits the Kelly
(and, in turn, the drill-string and bit) to be raised or lowered while drilling fluid is
pumped through the drill-string. The simultaneous lowering of the drill-string while
pumping fluid is critical to the drilling operation.
Photograph of Kelly hose
Kelly Spinner
Is the mechanical device for rotating the Kelly. The Kelly spinner is typically pneumatic.
It is a relatively low torque device, useful only for the initial makeup of threaded tool
joints. It is not strong enough for proper torque of the tool joint or for rotating the drillstring itself. The Kelly spinner has largely replaced the infamous spinning chains, which
were responsible for numerous injuries on the rig floor.
Kick
A Kick is the flow of reservoir fluids into the wellbore during drilling operations. The
kick is physically caused by the pressure in the wellbore being less than that of the
formation fluids, thus causing flow. This condition of lower wellbore pressure than the
formation is caused in two ways. First, if the mud weight is too low, then the hydrostatic
pressure exerted on the formation by the fluid column may be insufficient to hold the
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formation fluid in the formation. This can happen if the mud density is suddenly
lightened or is not to specification to begin with, or if a drilled formation has a higher
pressure than anticipated. This type of kick might be called an underbalanced kick. The
second way a kick can occur is if dynamic and transient fluid pressure effects, usually
due to motion of the drill-string or casing, effectively lower the pressure in the wellbore
below that of the formation. This second kick type could be called an induced kick.
Kill
Is how to stop a well from flowing or having the ability to flow into the well-bore. Kill
procedures typically involve circulating reservoir fluids out of the wellbore or pumping
higher density mud into the wellbore, or both. In the case of an induced kick, where the
mud density is sufficient to kill the well but the reservoir has flowed as a result of pipe
movement, the driller must circulate the influx out of the wellbore. In the case of an
underbalanced kick, the driller must circulate the influx out and increase the density of
the drilling fluid. In the case of a producing well, a kill fluid with sufficient density to
overcome production of formation fluid is pumped into the well to stop the flow of
reservoir fluids.
Kill Line
A high-pressure pipe leading from an outlet on the BOP stack to the high-pressure rig
pumps. During normal well control operations, the Kill fluid is pumped through the drillstring and annular fluid is taken out of the well through the choke line to the choke,
which drops the fluid pressure to atmospheric pressure. If the drill-pipe is inaccessible, it
may be necessary to pump heavy drilling fluid in the top of the well, wait for the fluid to
fall under the force of gravity, and then remove fluid from the annulus. In such an
operation, while one high pressure line would suffice, it is more convenient to have two.
In addition, this provides a measure of redundancy for the operation. In floating offshore
operations, the choke and kill lines exit the subsea BOP stack and run along the outside
of the riser to the surface. The volumetric and frictional effects of these long choke and
kill lines must be taken into account to properly control the well.
Kill Pump
A high-pressure pump designated for well-kill purposes. Depending on the application,
the kill pump may need to be connected to a ready supply of kill fluid should well control
be required at short notice.
Kill Weight Fluid
Is the mud whose density is high enough to produce a hydrostatic pressure at the point of
influx in a wellbore and shut off flow into the well-bore. Kill-weight mud, when needed,
must be available quickly to avoid loss of control of the well or a blowout. Thus, it is
usually made by weighting up some of the mud in the system or in storage by adding
barite or hematite. Unless diluted in advance, the mud may become too thick to pump due
to high solids loading. A weight-up pilot test can identify if and how much dilution will
be needed in advance of adding weighting material to the mud in the pits.
Landing Collar
A component installed near the bottom of the casing string on which the cement plugs
land during the primary cementing operation. The internal components of the landing
collar are generally fabricated from plastics, cement and other drillable materials.
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Cement shoe and float
Leak-off
The magnitude of pressure exerted on a formation that causes fluid to be forced into the
formation. The fluid may be flowing into the pore spaces of the rock or into cracks
opened and propagated into the formation by the fluid pressure. This term is normally
associated with a test to determine the strength of the rock, commonly called a pressure
integrity test (PIT) or a leak-off test (LOT). During the test, a real-time plot of injected
fluid versus fluid pressure is plotted. The initial stable portion of this plot for most
wellbores is a straight line, within the limits of the measurements. The leak-off is the
point of permanent deflection from that straight portion. The well designer must then
either adjust plans for the well to this leak-off pressure, or if the design is sufficiently
conservative, proceed as planned.
Life of the Well
Is the period of time during which economically sustainable production levels may be
expected from an oil well. The anticipated well life and the characteristics of the reservoir
fluid are the two main factors in specifying the completion system components.
Lost Circulation (Drilling)
Is the reduced or total absence of fluid flow up the annulus when fluid is pumped through
the drill-string. Though the definitions of different operators vary, this reduction of flow
may generally be classified as seepage (less than 20 bbl/hr), partial lost returns (greater
than 20 bbl/hr but still some returns), and total lost returns (where no fluid comes out of
the annulus). In this severe latter case, the hole may not remain full of fluid even if the
pumps are turned off. If the hole does not remain full of fluid, the vertical height of the
fluid column is reduced and the pressure exerted on the open formations is reduced. This
in turn can result in another zone flowing into the wellbore, while the loss zone is taking
mud, or even a catastrophic loss of well control. Even in the two less severe forms, the
loss of fluid to the formation represents a financial loss that must be dealt with, and the
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impact of which is directly tied to the per barrel cost of the drilling fluid and the loss rate
over time.
Lost Circulation (Drilling Fluids)
Is the lack of mud returning to the surface after being pumped down a well. Lost
circulation occurs when the drill bit encounters natural fissures, fractures or caverns, and
mud flows into the newly available space. Lost circulation may also be caused by
applying more mud pressure (that is, drilling overbalanced) on the formation than it is
strong enough to withstand, thereby opening up a fracture into which mud flows.
Material-Balance Equation
Mathematical relationship between the densities and the corresponding volumes of
mixtures of liquid-solid slurries and clear fluid blends, such as drilling muds and
completion fluids. Assumptions are: (1) masses and volumes of components are additive
and (2) material is neither generated nor lost from the system. As a simple example,
below are the two material-balance equations for a three-component mixture of oil (o),
water (w) and solids (s), where V = volume percent, D = specific density and MW =
mixture weight. (This could represent a simple, weighted oil-base mud formulation.)
MW = DsVs + DoVo + DwVw
100% = Vs + Vo + Vw.
By solving these equations simultaneously, an unknown parameter can be found if other
parameters are known or can be estimated accurately. Material-balance equations are
used to derive formulations of muds, to calculate the amount of barite needed to weightup a mud, to determine the amount of water needed to dilute a mud, and to find the
volume of two or more muds to mix together to achieve a new mud weight and volume.
Material balance is also the basis for calculating solids content of muds based on mud
testing data
Maximum Treating Pressure
Maximum Treating Pressure is the surface-pump pressure limit below which a treatment
should be performed. The maximum treating pressure is determined to avoid fracturing
the formation or damaging completion components. The maximum treating pressure is
generally calculated to ensure that the pump-pressure limit equates to down-hole and
reservoir conditions that are within the design limits of the treatment.
Methane
Methane is the lightest and most abundant of the hydrocarbon gases and the principal
component of natural gas. Methane is a colorless, odorless gas that is stable under a wide
range of pressure and temperature conditions in the absence of other compounds.
Mouse Hole
An opening in the rig floor near the rotary table, but between the rotary table and the vdoor, that enables rapid connections while drilling. The mouse-hole is usually fitted
underneath with a length of casing, usually with a bottom. A joint of drill-pipe that will
be used next in the drilling operation is placed in the mouse-hole, box end up, by the rig
crew at a convenient time (immediately after the previous connection is made). When the
bit drills down and the Kelly is near the rotary table, another piece of drill-pipe must be
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added for drilling to continue. This next piece of pipe is standing in the mouse-hole when
the Kelly is screwed onto it. Then the Kelly and the joint of pipe in the mouse-hole are
raised to remove the pipe from the mouse-hole, the mouse-hole pipe screwed onto the
rest of the drill-string, and the drill-string lowered, rotated, and pumped through to
continue drilling. Another piece of pipe is put in the mouse-hole to await the next
connection.
Motor Man
A Motor Man is the member of the rig crew responsible for maintenance of the engines.
While all members of the rig crew help with major repairs, the motorman does routine
preventive maintenance and minor repairs.
Mud Balance
A Mud Balance is a device to measure density (weight) of mud, cement or other liquid or
slurry. A mud balance consists of a fixed-volume mud cup with a lid on one end of a
graduated beam and a counterweight on the other end. A slider-weight can be moved
along the beam, and a bubble indicates when the beam is level. Density is read at the
point where the slider-weight sits on the beam at level. A mud balance can calibrated
with water or other liquid of known density by adjusting the counter weight. Most
balances are not pressurized, but a pressurized mud balance operates in the same manner.
Mud Engineer
A Mud Engineer is the person responsible for testing the mud at a rig and for prescribing
mud treatments to maintain mud weight, properties and chemistry within recommended
limits. The mud engineer works closely with the rig supervisor to disseminate
information about mud properties and expected treatments and any changes that might be
needed. The mud engineer also works closely with the rig's derrick-man, who is charged
with making scheduled additions to the mud during his work period.
Mud Pit
A Mud Pit is a large tank that holds drilling fluid on the rig or at a mud-mixing plant. For
land rigs, most mud pits are rectangular steel construction, with partitions that hold about
200 barrels each. They are set in series for the active mud system. On most offshore rigs,
pits are constructed into the drilling vessel and are larger, holding up to 1000 barrels.
Circular pits are used at mixing plants and on some drilling rigs to improve mixing
efficiency and reduce dead spots that allow settling. Earthen mud pits were the earliest
type of mud pit, but environmental protection concern has led to less frequent use of open
pits in the ground. Today, earthen pits are used only to store used or waste mud and
cuttings prior to disposal and remediation of the site of the pit.
Mud Weight
Is the mass per unit volume of a drilling fluid, synonymous with Mud-Density. Weight is
reported in lbm/gal (also known as ppg), kg/m3 or g/cm3 (also called specific gravity or
SG), lb/ft3 or in hydrostatic gradient, lb/in2/ft (psi/ft) or pptf (psi/1000 ft). Mud weight
controls hydrostatic pressure in a wellbore and prevents unwanted flow into the well. The
weight of the mud also prevents collapse of casing and the open-hole. Excessive mud
weight can cause lost circulation by propagating, and then filling, fractures in the rock.
Mud weight (density) test procedures using a mud balance have been standardized and
published by the API.
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Multi-lateral Well
A Multilateral Well pertains to a well that has more than one branch radiating from the
main borehole. The term is also used to refer to the multilateral well itself.
Multi-lateral. A well that has more than one branch radiating from the main bore-hole is
called a multilateral well. Multilaterals can be relatively simple dual-opposing laterals or
complex multi-branched wells, as shown in these diagrams.
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Multilateral wells are classified from Level 1 to Level 6S according to the complexity of
the junctions. For example, a Level 4 multilateral well has casing and cement in both the
main wellbore and the junction.
Multiple Completion Well
Is a single wellbore having tubulars and equipment that enable production from two or
more reservoir zones. In most cases, at least two tubing strings will be used to provide the
necessary level of control and safety for production fluids. However, in some simple dual
completions, the second or upper zone is produced up the tubing-casing annulus. The
wellhead and surface flow-control facilities required for multiple completions can be
complex and costly; hence, multiple completions are relatively uncommon.
Nipple Down
To take apart, disassemble and otherwise prepare to move the rig or blowout preventers.
Nipple Up
To put together, connect parts and plumbing, or otherwise make ready for use. This term
is usually reserved for the installation of a blowout preventer stack.
Also:
This can also refer to the process of disassembling well-control or pressure-control
equipment on the wellhead. Depending on the configuration of the wellhead and casing
strings, it may be necessary to nipple-down and nipple-up the blowout preventer (BOP)
system as each casing string is run.
Offset Well
An existing wellbore close to a proposed well that provides information for planning the
proposed well. In planning development wells, there are usually numerous offsets, so a
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great deal is known about the subsurface geology and pressure regimes. In contrast, rank
wildcats have no close offsets, and planning is based on interpretations of seismic data,
distant offsets and prior experience. High-quality offset data are coveted by competent
well planners to optimize well designs. When lacking offset data, the well planner must
be more conservative in designing wells and include more contingencies.
Open-Hole
An open-hole is the uncased portion of a well. All wells, at least when first drilled, have
open-hole sections that the well planner must contend with. Prior to running casing, the
well planner must consider how the drilled rock will react to drilling fluids, pressures and
mechanical actions over time. The strength of the formation must also be considered. A
weak formation is likely to fracture, causing a loss of drilling mud to the formation and,
in extreme cases, a loss of hydrostatic head and potential well control problems. An
extremely high-pressure formation, even if not flowing, may have wellbore stability
problems. Once problems become difficult to manage, casing must be set and cemented
in place to isolate the formation from the rest of the wellbore. While most completions
are cased, some are open, especially in horizontal or extended-reach wells where it may
not be possible to cement casing efficiently.
Open-Hole Completion
A well completion that has no casing or liner set across the reservoir formation, allowing
the produced fluids to flow directly into the wellbore. This type of completion suffers the
major disadvantage that the sand-face is unsupported and may collapse. Also, without
any casing or liner installed, selective treatments or remedial work within the reservoir
section are more difficult.
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Open-Hole Packer
A type of packer designed for use in open-hole applications such as drill-stem testing.
Open-hole packers are typically configured with one large element that can be deformed
easily to contact the uneven formation surface, yet retain strength and sufficient integrity
to withstand the anticipated differential pressures.
Open-Hole Test
A drill-stem test performed in an open-hole section of the wellbore. The test once was a
popular method of assessing the productivity of exploration wells without the need to run
casing or liner across the reservoir interval. Open-hole testing now is less common
because of the risks and limits associated with fluid flow from an unsupported formation.
Opening Bomb
A device used in stage cementing to open the stage collar or diverting valve through
which the second or subsequent cement stage is placed. The opening bomb is dropped
down the casing string to land in a seat within the stage collar. Applying pump pressure
then activates a sliding collar that opens access ports, enabling circulation across the
upper casing interval.
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Stage cementing
Pack-Off
To “Pack-off” means to plug the wellbore around a drill-string. This can happen for a
variety of reasons, the most common being that either the drilling fluid is not properly
transporting cuttings out of the annulus or portions of the wellbore wall collapse around
the drill-string. When the well packs off, there is a sudden reduction or loss of the ability
to circulate, and high pump pressures follow. If prompt remedial action is not successful,
an expensive episode of stuck pipe can result. The term is also used in gravel packing to
describe the act of placing all the sand or gravel in the annulus.
Packer
A device that can be run into a wellbore with a smaller initial outside diameter that then
expands externally to seal the wellbore. Packers employ flexible, elastomeric elements
that expand. The two most common forms are the production or test packer and the
inflatable packer. The expansion of the former may be accomplished by squeezing the
elastomeric elements (somewhat doughnut shaped) between two plates, forcing the sides
to bulge outward. The expansion of the latter is accomplished by pumping a fluid into a
bladder, in much the same fashion as a balloon, but having more robust construction.
Production or test packers may be set in cased holes and inflatable packers are used in
open or cased holes. They may be run on wire-line, pipe or coiled tubing. Some packers
are designed to be removable, while others are permanent. Permanent packers are
constructed of materials that are easy to drill or mill out.
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Pill
A pill is a relatively small quantity (less than 200 bbl) of a special blend of drilling fluid
to accomplish a specific task that the regular drilling fluid cannot perform. Examples
include high-viscosity pills to help lift cuttings out of a vertical wellbore, freshwater pills
to dissolve encroaching salt formations, pipe-freeing pills to destroy filter cake and
relieve differential sticking forces and lost circulation material pills to plug a thief zone.
Primary Completion Components
The main elements of an oil or gas well, including the production tubing string, that
enable a particular type or design of completion to function as designed. The primary
completion components depend largely on the completion type, such as the pump and
motor assemblies in an electrical submersible pump completion.
Primary Cementing
Is the process of placing a cement sheath around a casing or liner string. The main
objectives of primary cementing operations include zonal isolation to prevent migration
of fluids in the annulus, support for the casing or liner string, and protection of the casing
string from corrosive formation fluids.
Production Casing
Is the casing string that is set across the reservoir interval and within which the primary
completion components are installed.
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Rabbit
A slang term for an internal drift diameter gauge typically used to check casing or tubing
joints before they are picked up and run into the wellbore. The drift diameter used
depends on the size and weight of the tubular being checked.
Racking Back Pipe
On a drilling rig is to place a stand of drill-pipe in the derrick when coming out of the
hole on a trip. The rig crew racks back pipe after the stand is unscrewed from the rest of
the drill-string. The floor crew then pushes the lower part of the stand away from the
rotary table to a position on one side of the Vee-door. While the floor crew is pushing the
pipe, the derrick-man gets ready to pull the top of the stand over into the fingerboards.
Once the rig crew has the pipe in the correct location, the driller slacks off on the drawworks, allowing the stand to rest on the drill-floor. This takes weight off of the elevators
previously supporting the pipe at the top, so the derrick-man can then unlatch the
elevators and pull the top of the pipe into the fingerboards for storage. Modern rig
designs have automated pipe-handling equipment that moves the pipe. When tripping the
pipe out of the hole, racking back pipe may occur every two to five minutes for hours at a
time.
Ram Blowout Preventer
Is a device that can be used to quickly seal the top of the well in the event of a well
control event (kick). A ram blowout preventer (BOP) consists of two halves of a cover
for the well that are split down the middle. Large-diameter hydraulic cylinders, normally
retracted, force the two halves of the cover together in the middle to seal the wellbore.
These covers are constructed of steel for strength and fitted with elastic rubber seal
components on the sealing surfaces. The halves of the covers, formally called ram blocks,
are available in a variety of configurations. In some designs, they are flat at the mating
surfaces to enable them to seal over an open wellbore. Other designs have a circular
cutout in the middle that corresponds to the diameter of the pipe in the hole to seal the
well when pipe is in the hole. These pipe rams effectively seal a limited range of pipe
diameters. Variable-bore rams are designed to seal a wider range of pipe diameters, albeit
at a sacrifice of other design criteria, notably element life and hang-off weight. Still other
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ram blocks are fitted with a tool steel-cutting surface to enable the ram BOPs to
completely shear through drill-pipe, hang the drill-string off on the ram blocks
themselves and seal the wellbore. Obviously, such an action limits future options and is
employed only as a last resort to regain pressure control of the wellbore. The various ram
blocks can be changed in the ram preventers, enabling the well team to optimize BOP
configuration for the particular hole section or operation in progress.
“Rat-hole”
A storage place for the Kelly, consisting of an opening in the rig floor fitted with a piece
of casing with an internal diameter larger than the outside diameter of the Kelly, but less
than that of the upper Kelly valve so that the Kelly may be lowered into the rat-hole until
the upper Kelly valve rests on the top of the piece of casing.
Rat-Hole
Extra hole drilled at the end of the well (beyond the last zone of interest) to ensure that
the zone of interest can be fully evaluated. The logging tool string may be as much as 120
ft [36.5 m] in length, so the rat-hole allows tools at the top of the logging string to reach
and measure the deepest zone of interest. In addition, there is usually a small amount of
extra hole drilled to allow for junk, hole fill-in and other conditions that may reduce the
effective depth of the well prior to running logging tools.
Rat-hole
Extra hole drilled at the bottom of the hole to leave expendable completion equipment,
such as the carriers for perforating gun charges.
Ream
To enlarge a wellbore. Reaming may be necessary for several reasons. Perhaps the most
common reason for reaming a section of a hole is that the hole was not drilled as large as
it should have been at the outset. This can occur when a bit has been worn down from its
original size, but might not be discovered until the bit is tripped out of the hole, and some
under-gauge hole has been drilled. Last, some plastic formations may slowly flow into
the wellbore over time, requiring the reaming operation to maintain the original hole size.
Reserve Pit
Any pit not part of the active (circulatory) system. The reserve pit may be used to store
spare or waste mud, base oil or brine. In operations on land, the reserve pit is usually a
plastic-lined, earthen pit, in which waste mud is stored until final disposal.
Reservoir
Is a subsurface body of rock having sufficient porosity and permeability to store and
transmit fluids. Sedimentary rocks are the most common reservoir rocks because they
have more porosity than most igneous and metamorphic rocks and form under
temperature conditions at which hydrocarbons can be preserved. A reservoir is a critical
component of a complete petroleum system.
Returns
Is the mud that comes back to the surface and exits through the flow-line after being
pumped down the drill-pipe. "Lost returns" is the situation in which some or all of the
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mud does not come back to the surface, which indicates that mud is being lost into weak,
fractured or vugular formations down-hole.
Reverse Circulation
Is the intentional pumping of wellbore fluids down the annulus and back up through the
drill-pipe. This is the opposite of the normal direction of fluid circulation in a wellbore.
Since the inside volume of the drill-pipe is considerably less than the volume of the
annulus outside of the drill-pipe, reverse circulation can bring bottom-hole fluids to the
surface faster than normal circulation for a given flow rate. Two potential hazards of
reverse circulation include lifting cuttings and other junk into the drill-string and the
rapid flow of reservoir fluids to the surface in a kick situation.
Rig Floor
The Rig Floor is a relatively small work area in which the rig crew conducts operations,
usually adding or removing drill-pipe to or from the drill-string. The rig floor is the most
dangerous location on the rig because heavy iron is moved around there. Drill-string
connections are made or broken on the drill-floor, and the driller's console for controlling
the major components of the rig are located there. Attached to the rig floor is a small
metal room, the doghouse, where the rig crew can meet, take breaks and take refuge from
the elements during idle times.
Roller Cone Bit
A tool designed to crush rock efficiently while incurring a minimal amount of wear on
the cutting surfaces. Invented by Howard Hughes, the roller-cone bit has conical cutters
or cones that have spiked teeth around them. As the drill-string is rotated, the bit cones
roll along the bottom of the hole in a circle. As they roll, new teeth come in contact with
the bottom of the hole, crushing the rock immediately below and around the bit tooth. As
the cone rolls, the tooth then lifts off the bottom of the hole and a high-velocity fluid jet
strikes the crushed rock chips to remove them from the bottom of the hole and up the
annulus. As this occurs, another tooth makes contact with the bottom of the hole and
creates new rock chips. Thus, the process of chipping the rock and removing the small
rock chips with the fluid jets is continuous. The teeth intermesh on the cones, which helps
clean the cones and enables larger teeth to be used. There are two main types of rollercone bits, steel milled-tooth bits and carbide insert bits.
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Rotary Drilling
A method of making hole that relies on continuous circular motion of the bit to break
rock at the bottom of the hole. This method, made popular after the discovery of the East
Texas Field by "Dad" Joiner in 1930, is much more efficient than the alternative, cable
tool drilling. Rotary drilling is a nearly continuous process, because cuttings are removed
as drilling fluids circulate through the bit and up the wellbore to the surface. Cable tool
operations are discontinuous and cuttings removal is inefficient. This difference in
efficiency becomes particularly significant as hole depth increases.
Rotary Table
The revolving or spinning section of the drill-floor that provides power to turn the drillstring in a clockwise direction (as viewed from above). The rotary motion and power are
transmitted through the Kelly bushing and the Kelly to the drill-string. When the drillstring is rotating, the drilling crew commonly describes the operation as simply, "rotating
to the right," "turning to the right," or, "rotating on bottom." Almost all rigs today have a
rotary table, either as primary or backup system for rotating the drill-string. Top-drive
technology, which allows continuous rotation of the drill-string, has replaced the rotary
table in certain operations. A few rigs are being built today with top-drive systems only,
and lack the traditional Kelly system.
Rough Neck
Is a low-ranking member of the drilling crew. The roughneck usually performs
semiskilled and unskilled manual labor that requires continual hard work in difficult
conditions for many hours. After roughnecks understand how the rig operates and
demonstrates their work ethic, they may be promoted to other positions in the crew.
Generically: Any member of the drilling crew. In conversational use, one might claim to
have "rough-necked" in one's youth. This might actually refer to roughneck duties, or to
one of the other crew positions, such as lead tong operator, motorman, derrick-man,
assistant driller or even driller.
Roustabout
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Is any unskilled manual laborer on the rig-site. A roustabout may be part of the drilling
contractor's employee workforce, or may be on location temporarily for special
operations. Roustabouts are commonly hired to ensure that the skilled personnel that run
an expensive drilling rig are not distracted by peripheral tasks, ranging from cleaning up
location to cleaning threads to digging trenches to scraping and painting rig components.
Although roustabouts typically work long hard days, this type of work can lead to more
steady employment on a rig crew.
Safety Joint
A weak spot in the drill-string. Such a weak spot sometimes is intentionally put into the
drill-string so that if tension in the drill-string exceeds a predetermined amount, the safety
joint will part and the rest of the drill-string will be salvageable. A safety joint is
commonly included in fishing strings and drill-stem testing equipment, where the fish
may be successfully caught by the fishing assembly, but tension to free the fish may
prove insurmountable. By having the safety joint in the hole, the fishing company
representative knows where the fishing string will part and what will be needed to latch
onto the top of this additional fish.
Saver Sub
Is a short length of drill collar that has male threads on one end and female on the other.
It is screwed onto the bottom of the Kelly or top-drive and onto the rest of the drill-string.
When the hole must be deepened, and pipe added to the drill-string, the threads are
unscrewed between the saver sub and the rest of the drill-string, as opposed to between
the Kelly or top-drive and the saver sub. This means that the connection between the
Kelly or top-drive and the saver sub rarely is used, and suffers minimal wear and tear,
whereas the lower connection is used in almost all cases and suffers the most wear and
tear. The saver sub is expendable and does not represent a major investment. However,
the Kelly or top-drive component threads are spared by use of a saver sub, and those
components represent a significant capital cost and considerable downtime when
replaced.
Scratcher
A device for cleaning mud and mud filter cake off of the wellbore wall when cementing
casing in the hole to ensure good contact and bonding between the cement and the
wellbore wall. The scratcher is a simple device, consisting of a band of steel that fits
around a joint of casing, and stiff wire fingers or cable loops sticking out in all directions
around the band (360-degree coverage). A scratcher resembles a bottlebrush, but its
diameter is greater than its height. Importantly, for scratchers to be effective, the casing
must be moved. This movement may be reciprocal motion in and out of the wellbore,
rotary motion, or both. In general, the more motion, the better the cement job will be.
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Scratcher: The wire loops in this photograph serve as scratchers. As the casing is moved
up and down or rotated in the hole, the scratchers clean mud and filter cake from the sides
of the hole, allowing the cement slurry to fill the annulus completely.
Sidetrack
To drill a secondary wellbore away from an original wellbore. A sidetracking operation
may be done intentionally or may occur accidentally. Intentional sidetracks might bypass
an unusable section of the original wellbore or explore a geologic feature nearby. In the
bypass case, the secondary wellbore is usually drilled substantially parallel to the original
well, which may be inaccessible due to an irretrievable fish, junk in the hole, or a
collapsed wellbore.
Note: A secondary wellbore drilled away from the original hole. It is possible to have
multiple sidetracks, each of which might be drilled for a different reason
Tail Cement
The last cement system pumped during primary cementing. The tail cement covers the
lower sections of the well, especially planned completion intervals, and is typically a
higher density than the lead slurry that precedes it.
Tie-back Liner (Rig Work-over)
A section of liner that is run from a liner hanger back to the wellhead after the initial liner
and hanger system have been installed and cemented. A tie-back liner may be required to
provide the necessary pressure capacity during a flow-test period or for special
treatments, and is typically not cemented in place. In some cases, a tie-back liner will be
installed as a remedial treatment when the integrity of the intermediate casing string is in
doubt.
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Casing strings
Tight Hole
A well that the operator requires be kept as secret as possible, especially the geologic
information. Exploration wells, especially rank wildcats, are often designated as tight.
Unfortunately, this designation is of questionable benefit in keeping the data secret.
Tongs
Large-capacity, self-locking wrenches used to grip drill-string components and apply
torque. As with opposing pipe wrenches for a plumber, the tongs must be used in
opposing pairs. As a matter of efficiency, one set of tongs is essentially tied off with a
cable or chain to the derrick, and the other is actively pulled with mechanical catheads.
The breakout tongs are the active tongs during breakout (or loosening) operations. The
makeup tongs are active during makeup (or tightening) operations.
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Photograph of tongs
Tool Joints
Are the enlarged and threaded ends of joints of drill-pipe. These components are
fabricated separately from the pipe body and welded onto the pipe at a manufacturing
facility. The tool joints provide high-strength, high-pressure threaded connections that are
sufficiently robust to survive the rigors of drilling and numerous cycles of tightening and
loosening at threads. Tool joints are usually made of steel that has been heat treated to a
higher strength than the steel of the tube body. The large-diameter section of the tool
joints provides a low stress area where pipe tongs are used to grip the pipe. Hence,
relatively small cuts caused by the pipe tongs do not significantly impair the strength or
life of the joint of drill-pipe.
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Diagram of a Tool Joint. The enlarged, threaded ends of drill-pipe ensure strong
connections that withstand high pressures. This diagram shows the enlargement, known
as upset, and the threads at the end of the joint.
Tool Pusher
Is the location supervisor for the drilling contractor. The tool-pusher is usually a senior,
experienced individual who has worked his way up through the ranks of the drilling crew
positions. His job is largely administrative, including ensuring that the rig has sufficient
materials, spare parts and skilled personnel to continue efficient operations. The toolpusher also serves as a trusted advisor to many personnel on the rig-site, including the
operator's representative, the company man.
Top-drive
Is a device that turns the drill-string. It consists of one or more motors (electric or
hydraulic) connected with appropriate gearing to a short section of pipe called a quill,
that in turn may be screwed into a saver sub or the drill-string itself. The top-drive is
suspended from the hook, so the rotary mechanism is free to travel up and down the
derrick. This is radically different from the more conventional rotary table and Kelly
method of turning the drill-string because it enables drilling to be done with three joint
stands instead of single joints of pipe. It also enables the driller to quickly engage the
pumps or the rotary while tripping pipe, which cannot be done easily with the Kelly
system. While not a panacea, modern top-drives are a major improvement to drilling rig
technology and are a large contributor to the ability to drill more difficult extended-reach
wellbores. In addition, the top-drive enables drillers to minimize both frequency and cost
per incident of stuck pipe.
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Top-drive. The yellow top-drive assembly in this photograph is suspended from the
yellow hook. The top-drive can turn the drill-string during trips, so potential for stuck
pipe is reduced.
Tour (Pronounced Tower)
Is a work shift of a drilling crew. Drilling operations usually occur around the clock
because of the cost to rent a rig. As a result, there are usually two separate crews working
twelve-hour tours to keep the operation going. Some companies prefer three eight-hour
tours. The graveyard tour is the overnight shift or the shift that begins at midnight.
Tripping Pipe
Is the act of pulling the drill-string out of the hole or replacing it in the hole. A pipe trip is
usually done because the bit has dulled or has otherwise ceased to drill efficiently and
must be replaced.
Tubulars
A generic term pertaining to any type of oilfield pipe, such as drill pipe, drill collars, pup
joints, casing, production tubing and pipelines.
Weight Indicator
One of the instruments that the driller uses to monitor and improve the operating
efficiencies of the drilling operation. The actual measurement of weight is made with a
hydraulic gauge attached to the dead line of the drilling line. As tension increases in the
drilling line, more hydraulic fluid is forced through the instrument, turning the hands of
the indicator. The weight that is measured includes everything exerting tension on the
wire rope, including the traveling blocks and cable itself. Hence, to have an accurate
weight measurement of the drill-string, the driller must first make a zero offset
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adjustment to account for the traveling blocks and items other than the drill-string. Then
the indicated weight will represent the drill-string (drill-pipe and bottom-hole assembly).
However, the driller is only nominally interested in this weight for most operations. The
weight of interest is the weight applied to the bit on the bottom of the hole. The driller
could simply take the rotating and hanging off bottom weight, say 300,000 pounds
[136,200 kg], and subtract from that the amount of rotating on bottom weight, say
250,000 pounds [113,500 kg], to get a bit weight of 50,000 pounds [22,700 kg].
However, most rigs are equipped with a weight indicator that has a second indicator dial
that can be set to read zero ("zeroed") with the drill-string hanging free, and works
backwards from the main indicator dial. After proper zeroing, any weight set on bottom
(that takes weight away from the main dial), has the effect of adding weight to this
secondary dial, so that the driller can read weight on bit directly from the dial.
Weight indicator. The driller monitors the weight indicator to maximize drilling
efficiency. The close-up photograph of the dial shows that weights are measured in
thousands of pounds. In this case, the string weight is 130,000 pounds [59,020 kg].
Well Control
The technology focused on maintaining pressure on open formations (that is, exposed to
the wellbore) to prevent or direct the flow of formation fluids into the wellbore. This
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technology encompasses the estimation of formation fluid pressures, the strength of the
subsurface formations and the use of casing and mud density to offset those pressures in a
predictable fashion. Also included are operational procedures to safely stop a well from
flowing should an influx of formation fluid occur. To conduct well-control procedures,
large valves are installed at the top of the well to enable well-site personnel to close the
well if necessary.
Work-over
The process of performing major maintenance or remedial treatments on an oil or gas
well. In many cases, work-over implies the removal and replacement of the production
tubing string after the well has been killed and a work-over rig has been placed on
location. Through-tubing work-over operations, using coiled tubing, snubbing or slickline equipment, are routinely conducted to complete treatments or well service activities
that avoid a full work-over where the tubing is removed. This operation saves
considerable time and expense.
Worm (Weevil)
A new, completely inexperienced member of the drilling crew. Such a crewmember is
stereotyped as prone to making mistakes and being injured, and typically endures pranks
played on him by the drilling crew. While the terms weevil and its close cousin, worm,
are used widely, they are labels of inexperience, rather than derogatory terms.
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Fluids
Acid
A generic term used to describe a treatment fluid typically comprising hydrochloric acid
and a blend of acid additives. Acid treatments are commonly designed to include a range
of acid types or blends, such as acetic, formic, hydrochloric, hydrofluoric and fluroboric
acids. Applications for the various acid types or blends are based on the reaction
characteristics of the prepared treatment fluid.
Antifoam Agent
A chemical additive used to prevent the formation of foam during the preparation of a
treatment fluid or slurries at surface. Excess foam created during the mixing process may
cause handling and pumping difficulties and may interfere with the performance or
quality control of the mixed fluid. Antifoam agents may also be used to break foams
returned from the wellbore, following a treatment, in preparation for disposal of the
fluids.
Brine
Saline liquid usually used in completion operations and, increasingly, when penetrating a
pay zone. Brines are preferred because they have higher densities than fresh water but
lack solid particles that might damage producible formations. Classes of brines include
chloride brines (calcium and sodium), bromides and formats.
Calcium Bromide
A compound of formula CaBr2 used in conjunction with calcium chloride [CaCl3] in
completion operations to make solids-free brines with densities in the range 11.5 to 14.5
ppg.
Calcium Carbonate
A compound with formula CaCO3 that occurs naturally as limestone. Ground and sized
calcium carbonate is used to increase mud density to about 12 lbm/gal [1.44 kg/m3], and
is preferable to barite because it is acid-soluble and can be dissolved with hydrochloric
acid to clean up production zones. Its primary use today is as a bridging material in drillin, completion and work-over fluids. Sized calcium carbonate particles, along with
polymers, control fluid loss in brines or drill-in, completion and work-over fluids.
Insoluble calcium carbonate is the precipitated byproduct of mud treatments used for
removal of either Ca+2 or CO3-2 by addition of the other ion.
Calcium Chloride
A highly soluble calcium salt of formula CaCl2 used to make drilling and work-over
fluids or brines with a density range from 8.33 to 11.6 lb/gal at saturation. CaCl2 can be
blended with other brines, including sodium chloride [NaCl], calcium bromide [CaBr2]
and zinc bromide [ZnBr2]. Emulsification of CaCl2 brine as the internal phase of oil-base
or synthetic-base mud is an important use because the brine provides osmotic wellbore
stability while drilling water-sensitive shale zones.
Calcium Hydroxide
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A chemical with formula Ca(OH)2, commonly called slaked lime. Lime is used in lime
muds and as a treatment to remove carbonate ions. It is used as a stabilizing ingredient in
oil- and synthetic-base mud, essential to formation of fatty-acid soap emulsifiers. It is an
alkaline material that can be carried in excess to neutralize hydrogen sulfide [H2S] and
carbon dioxide [CO2].
Calcium Mud
A class of water-base drilling fluid that utilize dissolved Ca+2 as a component. Examples
are lime mud, gyp mud and calcium chloride [CaCl2] mud. The latter is rarely used, but is
based on solutions of CaCl2 that, in high concentration, can impart density up to 11.6
lbm/gal and has been touted as providing shale inhibition.
Dead Crude
Oil at sufficiently low pressure that contains no dissolved gas, or a relatively thick oil or
residue that has lost its volatile components.
Demulsifier
A chemical used to break emulsions (that is, to separate the two phases). The type of
demulsifier selected depends on the type of emulsion, either oil-in-water or water-in-oil.
Demulsifiers are used in the chemical analysis of oil and synthetic muds and to treat
produced hydrocarbons.
Dew Point
The dew point is the pressure at which the first condensate liquid comes out of solution in
a gas condensate. Many gas condensate reservoirs are saturated at initial conditions,
meaning that the dew point is equal to the initial reservoir pressure. Condensate
dissolution is called retrograde condensation because this is counter to the behavior of
pure substances, which vaporize when the pressure drops below the saturation pressure
under isothermal (constant temperature) conditions.
Diesel-oil Mud
Diesel-oil mud is an oil-base mud with diesel oil as its external phase. Diesel-oil mud is
the traditional oil mud and has a history of excellent performance for drilling difficult
wells. It has been used because the base oil is low-cost and widely available motor fuel.
In-gauge holes can be drilled through all types of shale, salt, gypsum and other difficult
strata using diesel-oil mud systems. It is often the mud of choice for drilling highpressure, high-temperature zones. Diesel-oil muds usually contain from 5 to 40 vol.%
emulsified brine water (except those that are specially designed to have none). The water
phase usually contains 20 to 40 wt.% dissolved calcium chloride for shale control.
Diesel-oil muds have been replaced in land drilling by mineral-oil muds and offshore by
synthetic-fluid muds. These newer muds have fewer health, safety and environmental
concerns compared to diesel oil.
Drilling Fluids
A general term that refers to various salts and salt mixtures dissolved in an aqueous
solution. Brine can be used more strictly, however, to refer to solutions of sodium
chloride. We prefer to use brine as a general term. The emulsified calcium chloride
[CaCl2] solution (or any other saline phase) in an oil mud is referred to as "brine" or
"brine phase." The oil/brine ratio, abbreviated OBR, is used to compare solids content
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and salinities of oil muds. Clear brines are salt solutions that have few or no suspended
solids.
Emulsion Mud
A water-base drilling fluid that contains dispersed oil or synthetic hydrocarbon as an
internal phase. Early emulsion muds used diesel or crude oil dispersed into alkaline
water-base muds. Synthetic liquids are now being substituted for oils in emulsion muds.
Water-base muds containing certain synthetic liquids can be discharged in the Gulf of
Mexico because they are environmentally safe and pass the EPA static sheen test and
mysid shrimp toxicity tests.
Glycol
Is a fluid with a series of alcohols with the general formula C2nH4n+2On+1. The simplest
member is ethylene glycol C2H6O2, widely used as antifreeze. Glycols may be used in
drilling fluids or production facilities as gas hydrate inhibitors.
Naphthene-base Crude Oil
Crude oil containing asphaltic materials but very little or no paraffin wax. This type of oil
is suitable for making gasoline, lubricating oil and asphalt. It is also called asphalt-base
crude.
Natural Gas
A naturally occurring mixture of hydrocarbon gases that is highly compressible and
expansible. Methane [CH4] is the chief constituent of most natural gas (constituting as
much as 85% of some natural gases), with lesser amounts of ethane [C2H6], propane
[C3H8], butane [C4H10] and pentane [C5H12]. Impurities can also be present in large
proportions, including carbon dioxide, helium, nitrogen and hydrogen sulfide.
Natural Gas Liquids
Components of natural gas that are liquid at surface in field facilities or in gas-processing
plants. Natural gas liquids can be classified according to their vapor pressures as low
(condensate), intermediate (natural gasoline) and high (liquefied petroleum gas) vapor
pressure.
Natural gas liquids include propane, butane, pentane, hexane and heptane, but not
methane and ethane, since these hydrocarbons need refrigeration to be liquefied. The
term is commonly abbreviated as NGL.
Natural Gasoline
Is a natural gas liquid with a vapor pressure intermediate between condensate and
liquefied petroleum gas. This liquid hydrocarbon mixture is recovered at normal pressure
and temperature and is much more volatile and unstable than commercial gasoline.
Neutralization
Neutralization is a chemical reaction between an acid and a base to form a salt and water.
Neutralization is used in the manufacture of mud products, removal of acidic
contaminants from muds and formation of emulsifiers in oil mud. Neutralization is used
in the test for alkalinity of mud and mud filtrate.
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Neutralizing Solution
A fluid prepared to counteract the corrosive effect of acids or acidic treatment fluids.
Neutralizing solutions generally are used when the components to be protected cannot be
adequately flushed or when there is a risk that residual fluids may cause problems
through prolonged exposure. Neutralizing solutions are commonly formulated with soda
ash to provide an inexpensive, non-damaging alkaline fluid that does not create excessive
disposal difficulties.
Nitrified Fluid
Nitrified fluid is a multiphase fluid incorporating a liquid base and gaseous nitrogen.
Nitrified fluids are frequently used in stimulation treatments to enhance the performance
of the treatment fluid and improve the cleanup process following the treatment.
Octanol
Octanol is an eight-carbon alcohol. Iso-octanol is used as a de-foamer for water muds.
Oil-base Mud
Is an invert-emulsion mud, or an emulsion whose continuous phase is oil. In the past, the
term referred to an oil mud containing less than about 5 vol. % water. This definition, at
the time, distinguished mud with less than 5 vol.% water from invert-emulsion oil muds,
which had more than 5 vol.% water. Today, this distinction is not practical because most
commercial oil muds can be formulated with more or less than 5 vol.% water using
essentially the same types of products.
Oil-base mud. Invert emulsion muds, or oil-base drilling fluids, typically contain
synthetic fluids, diesel oil or mineral oil without much water. When hydration of clay
formations is possible, oil-base drilling fluids are non-damaging to the reservoir.
Osmosis
Osmosis is the movement of water from one aqueous system to another through a semipermeable membrane. Osmotic movement is driven by activity differences between the
two systems and can be considered as a vapor-phase transfer. An oil mud acts as an
osmotic system. Emulsion film surrounding each brine droplet in an oil mud acts as semipermeable osmotic membrane and allows water molecules to pass back and forth, but
restricts ions and larger molecules. Clays in shale formations also are aqueous systems
that interact by osmosis with oil-mud droplets.
Oxygen Scavenger (Drilling)
Is a chemical that reacts with dissolved oxygen (O2) to reduce corrosion, such as sulfite
(SO3-2) and bisulfite (HSO3-) ions that combine with oxygen to form sulfate (SO4-2). This
is a redox reaction and requires a nickel or cobalt catalyst. Removal of air from a mud by
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de-foaming and mechanical degassing is an essential first step before a scavenger can
lower the dissolved oxygen content.
Oxygen Scavenger (Completions)
A chemical agent used in some brines and completion fluids to reduce corrosion resulting
from, or exacerbated by, dissolved oxygen. Oxygen scavengers capture the dissolved
oxygen in a harmless chemical reaction that renders the oxygen unavailable for corrosive
reactions. The use of oxygen scavengers is more critical in applications in which fluids
are to be circulated in the wellbore. Additional oxygen may be dissolved during agitation
at surface.
(Click to enlarge)
Paddle Blender
A type of fluid-mixing tank used in the preparation of treatment fluids or slurries that
provides the agitation to achieve a well-dispersed mixture. Paddle mixers are generally
equipped with rotating paddles that provide turbulence for mixing fluids and an action
that prevents the settling of solids prior to being pumped. Paddle blenders are also found
in Vac Trucks to keep fluids in solution.
Paraffin-Base Crude Oil
Is a crude oil containing paraffin wax but very few asphaltic materials. This type of oil is
suitable for motor lubricating oil and kerosene.
Paraffin Inhibitor
A chemical injected into the wellbore to prevent or minimize paraffin deposition. The
effectiveness of paraffin inhibitors is strongly dependent on crude oil composition.
Paraffin inhibitors must be introduced into the oil before the oil cools to its cloud point.
In additional, asphaltene composition should be determined before treatment because it
can reduce the effectiveness of the paraffin inhibitor. In some cases, the use of a paraffin
inhibitor can actually increase the rate of paraffin deposition because the stability of
colloidal asphaltenes is disturbed.
Perforating Fluid
A specially prepared fluid placed in the wellbore over the interval to be perforated. The
ideal fluid is clean and solids-free (filtered), and will not react to cause damaging by-
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products on contact with the reservoir formation. Perforating in a dirty fluid may result in
significant permeability damage that is difficult to treat and remove.
Potassium Mud
A class of mud that contain potassium ion (K+) dissolved in the water phase. Potassium
based mud is the most widely accepted water mud system for drilling water-sensitive
shale, especially hard, brittle shale. K+ ions attach to clay surfaces and lend stability to
shale exposed to drilling fluids by the bit. The ions also help hold the cuttings together,
minimizing dispersion into finer particles. The presence of Na+ ions counteracts the
benefits of K+ ions and should be minimized by using fresh water (not sea water) for
make-up water. With time, Na+, Ca+2 and other ions accumulate from ion exchange with
clays, making the mud less effective, but regular treatment to remove Ca+2 improves
polymer function. Potassium chloride, KCl, is the most widely used potassium source.
Others are potassium acetate, potassium carbonate, potassium lignite, potassium
hydroxide and potassium salt of PHPA. Use of bentonite clay is restricted because of its
strong affinity for K+. Instead, various polymers are used. XC polymer and PHPA are
used for rheology. For fluid-loss control, mixtures of starch and polyanionic cellulose are
often used. CM starch, HP starch, carboxymethylcellulose and sodium polyacrylate
(SPA) are also used. PHPA is widely used for shale encapsulation. Potassium, lime and
starch-like polymers have also been used as potassium mud systems. Although three API
methods exist for determining the K+ ion concentration, the centrifuge method (for K+
>5000 mg/L) is the most accepted field method, and essential for daily monitoring of
potassium in a mud. Regular additions of potassium salt maintain shale stability. K+ ion is
rapidly consumed while drilling shallow, soft and highly dispersive (gumbo) shales, but
maintaining sufficient K+ ion to stabilize gumbo can become expensive when drilling
large holes. Researchers, notably Dr. Dennis O'Brien and Dr. Martin Chenevert (while at
Exxon Production Research), evaluated different shale, their clay mineralogy and the
concentration of K+ needed to stabilize them. Potassium mud above about 1 wt.% K+ ion
usually fail the mysid shrimp (US EPA) bioassay test. Therefore, K-mud currently find
low acceptance in offshore drilling in USA waters.
Pre-hydrate
Is to mix with water and allow to react or yield in the water before use. Pre-hydrating is a
common technique for incorporating bentonite in cement slurry or drilling mud. Prehydration may also be done for convenience in cementing operations to allow mixing of
water containing the additives with powdered neat cement. Additives also may be prehydrated with mix water to avoid dry-blending the additives with cement.
Produced Water
Water containing salts in solution, such as sodium, calcium or bromides. Brine is
commonly produced along with oil. The disposal of oilfield brine is usually accomplished
by underground injection into salt-water saturated formations or by evaporation in
surface pits.
Primary Cementing
The first cementing operation performed to place a cement sheath around a casing or
liner. The main objectives of primary cementing include zonal isolation to prevent fluid
migration in the annulus, support for the casing or liner, and protection of the casing from
corrosive fluids.
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Saltwater Mud
A water mud containing varying amounts of dissolved sodium chloride, NaCl, as a major
component. Undissolved salt may also be present in saturated salt muds to increase
density beyond 10 lbm/gal or to act as a bridging agent over permeable zones. Starch and
starch derivatives for fluid-loss control and xanthan gums for hole-cleaning are among
the few highly effective additives for saltwater muds. Attapulgite and sepiolite are used in
saltwater muds only for cuttings lifting. The primary use of saltwater mud is to drill salt
strata that are prone to dissolution when exposed to other types of drilling fluid. A
saturated salt mud is used to drill salt to prevent hole enlargement. In hot, plastic, salt
zones, the hole may close inward unless extremely high mud weight is maintained. As an
alternative to high mud weight, maintaining undersaturation in the fluid allows controlled
leaching to offset hole closure by plastic flow. Sized salt particles in saturated saltwater
muds are used, along with polymers, to bridge over permeable production zones. The salt
can be removed later with a water flush. Salt solids can increase density beyond 10
lbm/gal, up to about 13 lbm/gal, if needed.
Scavenger
A treating chemical that is added to a drilling mud or other fluid to react with a
contaminant to change the contaminant to a less harmful compound. If a contaminant is
harmful at very low concentration, a scavenger must be able to remove the contaminant
to an even lower concentration to ensure safety.
Silicate Mud
A type of shale-inhibitive water mud that contains sodium or potassium silicate as the
inhibitive component. High pH is a necessary characteristic of silicate muds to control the
amount and type of polysilicates that are formed. Mud pH is controlled by addition of
NaOH (or KOH) and the appropriate silicate solution. Silicate anions and colloidal silica
gel combine to stabilize the wellbore by sealing micro-fractures, forming a silica layer on
shales and possibly acting as an osmotic membrane, which can produce in-gauge holes
through troublesome shale sections that otherwise might require an oil mud. Mud
containing up to 50 vol.% soluble sodium silicate was first used in the 1930s for control
of shale but suffered from gelation problems. In the 1990s, silicate muds were
reintroduced as a way to avoid using oil muds. The newer systems use lower silicate
concentrations and KCl or NaCl or both to contribute to shale control. This comeback
may succeed due to better solids control and proper use of silicate chemistry. Poor
lubricity and temperature tolerance are the main drawbacks.
Treatment Fluid
A fluid designed and prepared to resolve a specific wellbore or reservoir condition.
Treatment fluids are typically prepared at the well-site for a wide range of purposes, such
as stimulation, isolation or control of reservoir gas or water. Every treatment fluid is
intended for specific conditions and should be prepared and used as directed to ensure
reliable and predictable performance.
Weighted Mud
A mud that contains commercial weighting material such as barite or hematite. The
economic difference in weighted and unweighted muds is the cost of replacing weighting
material according to the solids control practices used. Solids control techniques, such as
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dilution or hydrocycloning, that can be economical in unweighted muds are not
necessarily economical for weighted muds, although centrifugation (incorrectly called
"barite recovery") is typically performed when using weighted muds to control mud
viscosity.
Well Completions Fluid
A water-based solution of inorganic salts used as a well-control fluid during the
completion and work-over phases of well operations. Brines are solids free, containing no
particles that might plug or damage a producing formation. In addition, the salts in brine
can inhibit undesirable formation reactions such as clay swelling. Brines are typically
formulated and prepared for specific conditions, with a range of salts available to achieve
densities ranging from 8.4 to over 20 lbm/gal (ppg) [1.0 to 2.4 g/cmo]. Common salts
used in the preparation of simple brine systems include sodium chloride, calcium chloride
and potassium chloride. More complex brine systems may contain zinc, bromide or
iodine salts. These brines are generally corrosive and costly.
Xylene
(CH3)2. Xylene is an excellent solvent, especially for aromatic solids such as asphaltic
materials. It is used as a solvent and emulsion breaker in work-over operations to clean
up reservoirs. In drilling mud testing, a 50/50 xylene/isopropanol (IPA) mixture had been
used to break oil-mud emulsions prior to titrations to measure alkalinity, chloride and
calcium. However, the xylene mixture has been replaced by a single material, propylene
glycol normal propyl ether (PNP), to break oil mud emulsions.
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