PAB2024
Drilling engineering
Petroleum Engineering Course
Lab report 2
Drilling fluid
Conducted on 26th of October 2010
Table of Contents
1-Introduction
2-Objectives
3-Procedures
4-Results
5-Discussion
6-Questions and answers
7-Refereneces
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1- INTRODUCTION
1
BASIC DRILLING SYSTEM
1.1 Circulating System
The main objective of circulation system is to pump fluid through the whole active fluid
system, including the borehole and all the surface tanks that constitute the primary system.
The complete, circuitous path that the drilling fluid travels starting at the: main rig pumps
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surface piping
standpipe
kelly hose (rotary)
kelly
drillpipe
drill collars
bit nozzles
openhole and casing strings
flowline
mud-cleaning equipment
mud tanks
positive displacement main rig pumps
Functions of Drilling Fluids:
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Lift-up cuttings
To cover the underground pressure
To restrain the well bore
To create mud cake and prevent filtrate loss
To lubricate drill bit and drill string
Down hole information gathering media and well logging
To transfer hydraulic force to downhole motor
1.2 Rotating System
The main objectives of this system is to create rotation force towards drill bit at the bottom
hole and provide helps when tightening and loosing pipe connection.
There are two types of rotating source:
1. Rotary Table
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The revolving or spinning section of the drillfloor 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 drillstring.
Almost all rigs today have a rotary table, either as primary or backup system for
rotating the drillstring. Top drive technology, which allows continuous rotation of
the drillstring, has replaced the rotary table in certain operations. A few rigs are
being built today with topdrive systems only, and lack the traditional kelly system.
2. Top Drive
A device that turns the drillstring. 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 drillstring itself. The
topdrive 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 drillstring 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.
1.3 Hoisting System
The main objective of this system is to provide lifting and dropping force towards drill string
and any components around rig floor.
Several components of this system are:
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crown block
travelling block
mast
substructure (sub)
prime mover
1.4 Pressure Control System
The objective of this system is to prevent blowout and maintain kick during drilling and
tripping. The equipment is called Blowout Preventer (BOP).
BOP is 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 (drillpipe,
casing or tubing) and others are fitted with hardened steel shearing surfaces that can actually
cut through drillpipe.
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1.5 Power System
The source of power for the rig location is provided by the Power System.
On modern rigs, the prime mover consists of one to four or more diesel engines. These
engines commonly produce several thousand horsepower. Typically, the diesel engines are
connected to electric generators.
The electrical power is then distributed by a silicon-controlled-rectifier (SCR) system around
the rig site. Rigs that convert diesel power to electricity are known as diesel electric rigs.
Older designs transmit power from the diesel engines to certain rig components (drawworks,
pumps and rotary table) through a system of mechanical belts, chains and clutches.
On these rigs, a smaller electric generator powers lighting and small electrical requirements.
These older rigs are referred to as mechanical rigs or more commonly, simply power rigs.
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KICK AND BLOW OUT
A kick is defined as any undesirable flow of formation fluids from the reservoir to the wellbore
that occurs as a result of a negative pressure differential across the formation face. Meanwhile,
Blow Out happens if the kick is reaching the surface and uncontrollable. Wells kick because the
reservoir pressure of an exposed permeable formation is higher than the wellbore pressure at that
depth.
Blow out can happen in almost every oil and gas operation such as:
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Drilling Operation
Work over Operation
Well Service Operation (Maintenance)
There are many situations which can produce this downhole condition. Among the most likely
and recurring are:
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Low density drilling fluid.
Abnormal reservoir pressure.
Swabbing.
Not keeping the hole full on trips.
Lost circulation
Kick indicators are classified into two groups: positive and secondary. Anytime the well
experiences a positive indicator of a kick, immediate action must be taken to shut-in the well.
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When a secondary indicator of a kick is identified, steps should be taken to verify if the well is
indeed kicking.
The "Positive Indicators of a Kick" are:
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Increase in Pit Volume
Increase in Flow rate
Immediate action should be taken to shut-in the well whenever these indicators are experienced.
It is not recommended to check for flow after a positive indicator has been identifed.
The "Secondary Indicators of a Kick" are:
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Decrease in Circulating Pressure
Gradual Increase in Drilling Rate
Drilling Breaks
Increase in Gas Cutting
Increase in Water Cutting or Chlorides
The occurence of any of these indicators should alert the Drilling Representative that the well
may be kicking, or is about to kick. These indicators should never be ignored. Instead, once
realized, steps should be taken to determine the reason for the indication.
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SWABBING
Swabbing is a condition that arises when pipe is pulled from the well and produces a temporary
bottomhole pressure reduction.
Many downhole conditions tend to increase the likelihood that a well will be swabbed-in when
pipe is pulled. Several of these are discussed below:
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Pulling Pipe Too Fast
Poor Mud Properties
Heaving or Swelling Formations
Large OD Tools
WELL CONTROL PROCEDURE (HARD SHUT IN * REMOTE
CHOKE IS ALWAYS CLOSE DURING DRILLING & TRIPPING)
4.1 SHUT-IN PROCEDURE WHILE DRILLING
1. When any indication is observed while drilling that the well maybe flowing, raise
the drill with pumps on until spaced out, stop rotating drill string.
2. Stop pumping and check for flow, if positive;
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3. Close annular or upper pipe rams.
4. Open BOP upstream choke valve.
5. Call supervisor and commence plotting a graph of shut in drill pipe & casing
pressure. Check pit volume again.
4.2 SHUT-IN PROCEDURE WHILE TRIPPING
1. When a possible sign is observed, set top tool joint in the slips.
2. Check for flow.
3. Install a full opening Safety valve on the drill pipe. Close the valve once it is
installed.
4. CLOSE annular BOP.
5. Open BOP upstream choke valve.
6. Alert supervisors.
7. Read and record pressures on SICP & SIDP
8. The operator’s representative will have to decide whether to kill in situ, or strip
back to bottom.
9. If operator decided to strip to bottom, stab IBOP (Gray valve) & open full
opening safety valve. Ready to strip drill string to bottom.
2-OBJECTIVE OF EXPERIMENT
We conducted the drilling fluid lab to determine many different things that will help in
our drilling process and to create a good quality mud. There were 4 experiments with
different objectives to be achieved.
-EXPERIMENT NO. 1 (MUD WEIGHT, MARSH FUNNEL VISCOSITY)
To determine and control the density of the drilling fluid using the Baroid mud
balance.
To find the viscosity of the fluid using the Marsh Funnel.
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-EXPERIMENT NO. 2 (MUD RHEOLOGY TEST)
To find how the fluid will flow under a variety of different conditions. And relate it to
the design of circulating systems.
To use The FANN Viscometer to determine the viscosity and gel strength of the fluid.
To calculate the yield strength by using the following formula:
YP = 300 RPM - Plastic Viscosity
-EXPERIMENT NO. 3 (FILTRATION, WALL BUILDING, AND RESISTIVITY)
To analyze and build the Standard API Filter Press device, and to know each of its
parts.
To observe the time taken for the fluid to leave the mud (filtration rate) at a certain
pressure and temperature.
To measure the mud cake thickness.
-EXPERIMENT NO. 4 (CONTROL OF MUD WEIGHT)
To know the effect of adding bentonite on mud properties for fresh
and salt water base mud.
To observe the effect of adding weight material (barite).
3- Procedures
EXPERIMENT NO. 1
MUD WEIGHT, MARSH FUNNEL VISCOSITY AND pH
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(A) MUD WEIGHT OR DENSITY TEST:
Procedures:
1. The lid was removed from the cup, and the cup completely was filled with the mud to
be tested.
2. The lid was replaced and rotated until firmly seated, there was some mud expelled
through the hole in the cup.
3. The mud was washed from the outside of the cup.
4. The balance arm was placed on the base, with the knife-edge resting on the fulcrum.
5. The rider was moved until the graduated arm leveled, as indicated by the level vial on
the beam.
6. At the left-hand edge of the rider, the density was read on either side of the lever in all
desired units without disturbing the rider.
7. Mud temperature corresponding to density had been noted.
(B) MUD VISCOSITY:
Procedures:
1. With the funnel in an upright position, the orifice was covered with a finger and
the freshly collected mud sample was poured through the screen into a clean, the
funnel was dried until the fluid level reached the bottom of the screen.
2. The finger was removed from the outlet and the time required for the mud to fill the
receiving vessel to the 1-quart (946 ml) level was measured.
3. The result was reported to the nearest second as Marsh Funnel Viscosity at the
temperature of the measurement in degrees Centigrade.
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(C) HYDROGEN ION CONCENTRATION (pH):
Procedures:
1. 2 samples of mud was taken from each of the mud tanks.
2. The samples were stirred for 2 minutes and the following properties were
determined:
(a) The Mud Weight
(b) Marsh Funnel Viscosity in seconds
(c) pH value using pH meter and Hydrion papers
EXPERIMENT NO. 2
MUD RHEOLOGY TEST
Viscosity, Gel Strength and Yield Point
(A) VISCOSITY:
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Procedures:
(A) VISCOSITY:
Procedures:
(A) VISCOSITY:
Procedures:
1. A recently agitated sample in the cup was placed, the upper housing of
the viscometer was tilted back, the cup was located under the sleeve, and the
upper housing was lowered to its normal position.
2. The knurled knob was turned between the rear support posts to raise or
lower the rotor sleeve until it immersed in the sample to the scribed line.
3. The sample was stirred for about 5 seconds at 600 RPM, and then the
RPM was selected desired for the best.
4. The dial reading was taken while it was stable.
5. The dial reading and RPM was recorded.
(B) GEL STRENGTH:
Procedures:
1. A sample at 600 RPM was stirred for 15 seconds.
2. The RPM knob was turned to the STOP position.
3. 10 seconds were taken as desired rest time.
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4. The RPM knob was switched to the GEL position.
5. The maximum deflection of the dial was recorded before the Gel breaks, as the Gel
strength in lb/100 ft2.
(C) YIELD POINT:
Procedures:
1. A recently agitated mud sample was obtained from each of mud tanks (1) and (2).
2. Using the FANN Viscometer, dial readings at 3, 300 and 600 RPM was obtained.
3. By means of the viscometer calculations procedure, the Apparent and Plastic
Viscosities, Yield Point and initial 10 sec was determined. And final 10-minutes Gel
Strength parameters.
EXPERIMENT NO. 3
FILTRATION, WALL BUILDING, AND RESISTIVITY
(A) FILTRATION:
Procedures:
1. The mud cell was detached from filter press frame.
2. Bottom of filter cell was removed, Right size filter paper was placed in the bottom of
the cell.
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3. The mud was introduced to be tested into cup assembly, the filter paper and screen
was put on top of mud tighten screw clamp.
4. With the air pressure valve closed, the mud cup assembly was clamped to the frame
while the filtrate outlet end finger was held tightly.
5. A graduated cylinder was placed underneath to collect filtrate.
6. Air pressure valve was opened and started timing at the same time.
7. cc of filtrate collected for specified intervals was reported up to 30 minutes.
8. The results had been tabulated in an appropriate table.
(B) WALL BUILD:
Procedures:
1. It reported in thirty-second of an inch in whole number. Vernier caliper was used to
measure the thickness, however, while measuring care was taken not to press vernier
jaw on mud cake to penetrate through.
2. Results on mud cake thickness was reported in whole number.
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EXPERIMENT NO. 4
CONTROL OF MUD WEIGHT
(A) EFFECT OF ADDING BENTONITE ON MUD PROPERTIES FOR FRESH AND SALT WATER
BASE MUD:
Procedures:
1. Batch of fresh water base mud 2, 4, 6 and 8 grams of bentonite was added to every
400 c.c and stirred for 10 minutes.
2. The density lb/gal, viscosity c.c. and yield point lb/100 ft was measured by using the
Rheometer for every batch.
3. 20.6 ml of 10% by weight salt water was added to every batch. It was Stirred for 5
minutes and step (2) had been repeated.
4. All the results for every batch were reported in a convenient table.
(B) EFFECT OF ADDING WEIGHT MATERIAL (BARITE):
Procedures:
1. The amount of barite required to increase the density of each
batch from 8.6 ppg to 9, 10, 11 and 12 ppg was calculated and listed.
2. 400 cc of original base mud were obtained at density 8.6
3. The calculated amount of barite were added to each batch, stirred for about 2
minutes ,and the Apparent ,Plastic Viscosities and Yield Point were measured.
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4. step 3 for Salt water-base mud had been repeated.
5. The results were tabulated.
(C) WATER-BACK (ADDING WATER TO A CHEMICALLY TREATED MUD):
Procedures:
1. A 350 c.c. of water base mud of 13.5 ppg weight and 9.5 pH were obtained.
2. Water was added incrementally and the Mud weight was measured every time to
reach 10.5 ppg and same (9.5) pH.
3. The viscosity and gel-strength was measured and checked for any change.
4. The results were tabulated.
4- RESULTS
EXPERIMENT 1
Sample No.
Mud Weight (ppg)
Marsh Funnel Viscosity (sec)
Average(sec)
1
8.5
17.28
17.30
17.25
17.28
2
9.1
17.84
17.78
18.04
17.89
EXPERIMENT 2
Data recorded from the FANN (rotational viscometer):
Shear rates
600RPM
300RPM
200RPM
Sample1
17
10.5
9
Sample 2
23
16
13
14
100RPM
6RPM
3RPM
6
2
1
9
7
5
Rheological Calculations:
1. Plastic viscosity (in centipoise-up)
Plastic viscosity=µp = 600RPM reading – 300 RPM reading
So for Sample 1:
Plastic viscosity= µp = 17 – 10.5 = 7.5 cp.
For Sample 2:
Plastic viscosity=µp = 23 – 16 = 7 cp.
2. Apparent viscosity (in centipoise-up)
Apparent viscosity= µa =
600 RPM reading
2
So for Sample 1:
Apparent viscosity =. µa =
17
2
= 8.5 cp.
23
2
= 11.5 cp.
For Sample 2:
Apparent viscosity = µa =
3. Yield point (in Ib/100 ft2)
Yield point = Y.P. = 300 RPM Reading – plastic viscosity
So for Sample 1:
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Yield point = Y.P. = 10.5 – 7.5 = 3 Ib/100 ft2
For Sample 2:
Yield point = Y.P. = 16 – 7 = 9 Ib/100 ft2
For the gel strength it is measured when the RPM= 3 RPM:
Recorded data
10 seconds
10
20
Sample 1
Sample 2
10 minutes
14
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Gel strength calculation (dynes/cm2):
1. Sample 1:
A) 10 seconds: gel strength = Ib/100ft2 × 5.077 = 10×5.077 = 50.77
dynes/cm2
B) 10 minutes: gel strength = Ib/100ft2 × 5.077 = 14×5.077 = 71.078
dynes/cm2
2. Sample 2:
A) 10 seconds: gel strength = Ib/100ft2 × 5.077 = 20×5.077= 101.54
dynes/cm2
B) 10 minutes: gel strength = Ib/100ft2 × 5.077 = 27×5.077 = 137.079
dynes/cm2
VISCOSITY CP
Gel strength Ib/100 ft^2
Sample NO.
initial 10
initial 10
600
300
µp
µa
YP Ib/100 ft^2
sec Gel
min. Gel
1
17
10.5
7.5
8.5
3
10
14
2
23
16
7
11.5
9
20
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EXPERIMENT 3
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Volume of water displaced by mud cake:
Time (minutes)
Volume of water (mL)
3
4.5
6
7
9
9
12
10.5
15
12
18
13
21
14
24
15
27
16
30
17
17
Time (minute)
18
16
14
12
10
Volume of water (ml)
8
6
4
2
0
3
6
9
12
15
Mud cake thickness readings:
Readings
1
2
3
Thickness
1.96 mm
2.25mm
2.18 mm
SAMPLE CALCULATION
Average reading at different spots of the mud cake:
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18
21
24
27
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Formula:
(reading 1 + reading 2 + reading 3)
Average
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Average thickness =
1.96mm  2.25mm  2.18mm
2.13mm
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EXPERIMENT 4
Regarding to the formula above,
WtB =
4.3 * VO (  f   O )
B   f
However, we also get the same result (mud weight) without using density by
formula as below:
Weight of Barite = 1470 (W2 – W1) / (35 – W2)
W2 – density of mud after adding barite , ppg
W1 – density of mud before adding barite, ppg
Thus, weight of Barite = 1470(9.1-8.5 / (35-9.1) = 34.05 g
After calculation, Barite weight is 34.05 g Barite need to be added to obtain density of
9.1 ppg for mixture.
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5- Discussion
The first experiment was to create a water-based drilling fluid with a certain composition. The
specified component was water and bentonite. 22, 5 grams of bentonite was added to 350 ml of
water. The fluid is then measured for its weight and viscosity. The weight was calculated
theoretically as well as using the densimeter whereas the viscosity was measured using the
Marsh Funnel viscometer. As many errors could have taken place for the viscosity measurement,
an average of 3 readings was taken. This was done for the two samples that were made.
Whereby the second sample was specified to have a weight of nine ppg by adding Barite to the
fluid.
The second experiment was to measure the plastic viscosity of the fluid. The device used for this
experiment was the FANN (rotational viscometer). Plastic Viscosity (PV) is the resistance of fluid
to flow. In the field, we can get the PV from a viscometer. Typically, the viscometer is utilized to
measure shear rates at 600, 300, 200, 100, 6, and 3 revolutions per minute (rpm).
We can calculate the plastic viscosity from the difference between the 600 and 300 rpm reading.
The formula looks like this:
Plastic Viscosity (PV) = Reading at 600 rpm – Reading at 300 rpm
The unit of PV is Centi Poise (CP).
For example, you have these values from a viscometer.
Reading at 600 rpm = 17
Reading at 300 rpm = 10.5
Plastic Viscosity (PV) = 17 – 10.5 = 6.5 CP
Any increase in solid content in drilling mud as Bartie, drill solid, lost circulation material, etc will
result in higher the plastic viscosity. In order to lower the PV, you must reduce the solid content
that can be achieved by using solid control equipment and/or diluting drilling mud with base
fluid. With increasing temperate while drilling deeper, the plastic viscosity of the drilling mud will
decrease because the viscosity of the base fluid decreases.
Normally, the higher mud weight, the higher PV will be. However, if you have an increasing trend
of PV without mud weight change, it means that there is an increase in ultra-fine drill solid
content in the mud system. Moreover, if you use oil base mud, please keep in mind that
emulsified water in oil base drilling fluid will act like a solid, and it will increase the plastic
viscosity dramatically.
Several impacts of PV on drilling operation are as follows;
Equivalent Circulating Density (ECD) – The more PV you have, the higher ECD will be.
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Surge and Swab Pressure – The PV has the same effect as ECD. If the PV increases, surge and
swab pressure will increase.
Differential Sticking – A chance for differential sticking will increase, especially in water base
mud, when the plastic viscosity increases because of increases in solid content.
Rate of Penetration (ROP) – The ROP will be directly affected by the plastic viscosity. If you drill a
well with the high PV drilling mud, you will drill at slower ROP than low PV mud.
Apparent viscosity is a rheological property calculated from rheometer readings performed by a
Mud engineer on drilling fluid. It is normally abbreviated as AV. It is expressed in cP (Centipoise).
Centipoise is the amount of force required to move one layer of fluid in relation to another. One
centipoise is equal to one hundredth of a poise.
For experiment 3, the amount of displaced water was measured. This is to simulate the fluid loss
within the drilling operation. A reading was taken every 3 minutes. The rate of the fluid loss was
decreasing with time. Which is what is expected as the thicker the fluid is, the harder it will be
for the fluid to escape. And mud cake was also measured at the end.
6 -Questions and answers
EXPERIMENT NO. 1
1. List any five (5) very important functions of the drilling fluid?
# Lifts soil/rock cuttings from the bottom of the borehole and carry them to a settling pit;
# allows cuttings to drop out in the mud pit so that they are not re-circulated (influenced
by mud thickness, flow rate in the settling pits and shape/size of the pits);
# prevent cuttings from rapidly settling while another length of drill pipe is being added (if
cuttings drop too fast, they can build-up on top of the bit and seize it in the hole);
# creates a film of small particles on the borehole wall to prevent caving and to ensure
that the upward-flowing stream of drilling fluid does not erode the adjacent formation;
# Seal the borehole wall to reduce fluid loss (minimizing volumes of drilling fluid is
especially important in dry areas where water must be carried from far away);
# cool and clean the drill bit
2. What requirements should drilling fluids meet?
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The density of the drilling fluid should be maintained so that it will provide an
adequate hydrostatic pressure to prevent formation fluids from entering the
borehole. Also the viscosity of the drilling fluid needs to be in an appropriate
value so that the cuttings from the borehole can be lifted upward to the surface. It
shouldn’t pollutant to the environment and must meet governmental requirements
for all the substances used in it.
3. Using the mud weights (ppg) obtained for Samples #1 and 2 of your
Experiments, calculate, how much hydrostatic pressure that each sample
will exert on a formation at a depth of 10,000 ft.
For sample 1:
P= 0.052* 8.5 ppg* 10000 ft= 2125 psi
For sample 2:
P= 0.052* 9.1 ppg* 10000ft= 4732 psi
4. What is the difference between over-balance and under-balance?
Overbalance is the condition where by the pressure in the well bore is greater
than the formation pressure while under balance is a condition where by the
pressure in the well bore is lower than the formation pressure. Also It is a drilling
technique used to reduce the chip holding pressure when it be forced and make
a difficulties to remove a part of rock by bit through rotary carbon steel teeth bit
and by weight on bit , it used the UBD to make a secondary annulus by using
another casing like tie back to divided the annulus to two part to relief the
hydrostatic column drilling fluid pressure and that will reduce the chip holding
pressure and will be treat even the kicks without breaking the drilling operation to
treat the kick off well.
5. Estimate the mud weight needed to balance a formation pressure
equivalent to 10,000ft depth with 0.561 psi/ft pressure gradient.
P formation = P mud
10,000 ft x 0.561psi/ft = 0.0052 x Mud Weight x 10,000ft
Mud Weight = 107.88ppg
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EXPERIMENT NO. 2
1)
a. What is Plastic Viscosity?
Plastic viscosity is the shearing stress in excess of yield point that will induce a
unit rate of shear. Mud is composed of solids that contribute to apparent
viscosity; Plastic viscosity is that part of flow resistance caused by mechanical
friction. This friction occurs (1) between the solids in the mud, (2) between the
solids and the liquid that surrounds them, and (3) with the searing of the liquid
itself. For practical field purposes, however, plastic viscosity depends upon the
concentration, size and shape of mud solids.
b. What does it characterize?
When the plastic viscosity of the mud is low that means the mud is capable of
drilling rabidly because of the low viscosity mud exciting the drilling bit in other
hand if the plastic viscosity is high that means the mud is drilling slower and this
caused by excess colloidal solids and we can solve that by adding or dilute the
mud.
c. What is the difference between the Plastic Viscosity and Apparent
Viscosity of a drilling fluid?
Apparent viscosity is a rheological property calculated from rheometer
readings performed by a Mud engineer on drilling fluid. It is normally abbreviated
as AV. It is expressed in cp (Centipoise). Centipoise is the amount of force
required to move one layer of fluid in relation to another. One centipoise is equal
to one hundredth of a poise. The viscosity of a fluid measured at the shear rate
specified by API. In the Bingham plastic rheology model, apparent velocity is
one-half of the dial reading at 600rpm using a direct-indicating, rotational
viscometer. While plastic viscosity is an absolute flow property indicating the flow
resistance of certain types of fluids. It is a measure of shearing stress.
2.
Which role does Gel strength play in the drilling process?
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It’s a measure of a fluid’s ability to hold particles in suspension. Gel strength is
measured on a concentric cylinder viscometer. And it helps to determine the
amount of mud cake produced during the drilling process.
3. What type of fluids does drilling fluid belong to?
The drilling fluid belongs to the non-Newtonian (Plastic fluids) viscosity type .
It should also be noted that;
There are several types of drilling fluids used depending on the drilling conditions
encountered:

Water-based muds are used most frequently. The base may be either:
o Colloidal clay
o Clay and polymer
o polymer

Non water base
o Synthetic Fluid
o Diesel Oil
o Mineral Oil

Pneumatic Mud
o Dry Gas
o Mist
o Foam
o Gasified Mud
4)
a. What is the Yield Point?
Yield point is a parameter of the Bingham plastic model. Yield point is the yield
stress extrapolated to a shear rate of zero. Yield point is a measure of the
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electro-chemical or attractive forces in the mud under flow (dynamic) conditions.
By definition the yield strength or yield point of a material is defined as the stress
at which a material begins to deform plastically. Prior to yield point the material
will deform elastically and will return to its original shape when the applied stress
is removed. Once the yield point is passed some fraction of the deformation will
be permanent and non-reversible.
b. What does it characterize?
A high yield point of the mud implies a non-Newtonian fluid, one that carries
cuttings better than a mud fluid of similar density but lower yield point. Yield point
is lowered by adding deflocculated to a clay-based mud and increased by adding
freshly dispersed clay or a flocculent, such as lime. also we can add that It is
measure of the attractive forces between active clay particles in mud under
flowing conditions. It is used to evaluate the ability of a mud to lift cuttings out of
annulus. A higher YP implies that drilling fluid has a ability to carry cuttings better
than a fluid of similar density but lower YP.
C. what is difference between Gel strength and yield point of a drilling
mud?
Gel strength is a status –dependant property of a mud. Its value depends on
how well the gel is formed. In the field, the pressure surge caused by mud
strength can be avoided by rotating drill string to break the gel before start of
pumping. YP is not a status-dependant property of a mud. The value of YP may
vary with temperature and pressure. However, the pressure changes at the
start/stop of pumping can be avoided with non-zero YP by any mechanical
means. YP is similar to mud gel strength in causing a sudden pressure change at
the start of pumping. However, the major difference between YP and gel strength
in term of hydraulics is that gel strength will not exist once the fluid is moving and
the gel has been broken, while the effect of YP will not disappear when the fluid
is moving.
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EXPERIMENT NO. 4
1. List the advantages obtained by adding weighting material to mud.
1. It will minimize the formation damage as the formation will not collapse to the
wellbore due to high endurance given by the higher density if mud
2. The added weighting material will maintain the wellbore stability when the
pressure is high that the ordinary mud cannot stand it
3. It will reduce the usage of more betonies to increase the density
4. The added weighting material will increase the density and can control the
higher formation pressure as the mud is going down.
2. List three names of weighting material.
1) Barite
2) Siderite
3) Hematite
4) Ilmenite
3. What are the disadvantages of adding solids to the water based mud?
1. The drilling mud will be more difficult to be pumped and greater velocity is
needed to move the mud.
2. It will easily cause unwanted ppg addition
3. Will cause the instability of the density and viscosity of the mud
4. It will disturb the formation of a nice smooth mud cake.
5. The cuttings are less likely to settle out in the mud pit as a denser fluid has
greater buoyancy
6. It might increase the pressure on the formation and cause a thicker filter cake.
This might contribute to problems like stuck pipe. As a result, this may incur a
higher expense in maintenance.
4. Give reasons for adding water to your mud?
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1. To decrease the viscosity as high viscosity will damage the formation and the
well.
2. To dilute the mud and decrease mud density. This will avoid the loss of
circulation and to minimize formation damage
3. To decrease the density and the viscosity of the mud in general.
7-Refereneces

Drilling engineering lecture notes PAB2024

http://en.wikipedia.org/wiki/Drilling_fluid
Retrieved on 29/10/2010

http://www.glossary.oilfield.slb.com/Display.cfm?Term=drilling%20fluid
Retrieved on 29/10/2010

Drilling Engineering by Jamal J. Azar & G. Robello Samuel

http://drillingcontractor.org/understanding-yield-point-effect-on-pressuresurges-critical-to-managing-deep-difficult-mpd-wells-1933
Retrieved on 29/10/2010
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