Rotary Drilling Rig
The most common drilling rigs in use today are rotary
drilling rigs. Their main tasks are to create rotation of the
drill string and facilities to advance and lift the drill string as
well as casings and special equipment into and out of the
hole drilled.
The main components of a rotary drilling rig can be seen in
following picture
Rotary Drilling Rig
In general, rotary rigs can be distinguished
into:
Land rigs:
Conventional rigs:
Small land rigs,
Medium land rigs,
Large land rigs,
Mobile rigs:
Portable mast,
Jacknife,
In general, rotary rigs can be distinguished
into:
Offshore rigs:
Bottom anchored rigs:
Artificial Island,
TLP,
Submersible,
Jack up,
Concrete-structured, etc.,
Floating rigs:
Drillship,
Semi-submersible,
Barge
For offshore rigs, factors like water depth, expected sea
states, winds and currents as well as location (supply
time) have to be considered as well.
Rig Power System
The power system of a rotary drilling rig has to supply the
following main components:
(1) Rotary system,
(2) Hoisting system and
(3) Drilling fluid circulation system.
In addition, auxiliaries like the blowout preventer,
water pumps, rig lighting system, etc. have to be powered.
Rig Power System
Since the largest power consumers on a rotary drilling rig
are the hoisting and the circulation system, these
components
determine
mainly
the
total
power
requirements. At ordinary drilling operations, the hoisting
(lifting and lowering of the drill string, casings, etc.) and
the circulation system are not operated at the same time.
Therefore the same engines can be engaged to perform both
functions.
Rig Power System
The power itself is either generated at the rig site using
internal-combustion diesel engines, or taken as electric
power supply from existing power lines.
The raw power is then transmitted to the operating
equipment via:
(1) Mechanical drives,
(2) Direct current (DC) or
(3) Alternating current (AC) applying a silicon-controlled
rectifier (SCR).
Most of the newer rigs using the AC SCR systems. As
guideline, power requirements for most rigs are between
1,000 to 3,000 [hp].
Hoisting System
The main task of the hoisting system is to lower and raise the
drill string, casings, and other subsurface equipment into or
out of the well.
The hoisting equipment itself consists of:
(1) Draw works,
(2) Fast line,
(3) Crown block,
(4) Travelling block,
(5) Dead line,
(6) Deal line anchor,
(7) Storage reel,
(8) Hook and
(9) Derrick,
see following sketch,
Hoisting System
Hoisting System
Hoisting System
Hoisting System
Draw works
The purpose of the draw works is to provide the hoisting
and breaking power to lift and lower the heavy weights of
drill string and casings.
The draw works itself consists of:
(1) Drum,
(2) Brakes,
(3) Transmission and
(4) Catheads
The drum provides the movement of the drilling line which
in turn lifts and lowers the travelling block and
consequently lifts or lowers the loads on the hook. The
breaking torque, supplied by the drum, has to be strong
enough to be able to stop and hold the heavy loads of the
drilling line when lowered at high speed.
Draw works
Circulation System
The principle components of the mud circulation system
are:
(1) mud pumps,
(2) flow lines,
(3) drill pipe,
(4) nozzles,
(5) mud pits and tanks (settling tank, mixing tank, suction
tank),
(6) mud mixing equipment (mud mixing hopper) and
(7)contaminant
removal
equipment
(shale
shaker,
desander, desilter, degasser)
Circulation System
The flow of circulated drilling mud can be described as from
the mud pit (storage of mud) via the mud mixing hopper,
where various additives like weighting material etc. can be
mixed into the mud, or the suction line to the mud pumps.
At the mud pumps the mud is pressured up to the required
mud pressure value. From the mud pumps the mud is
pushed through the stand pipe (a pipe fixed mounted at the
derrick), the rotary hose (flexible connection that allows the
fed of the mud into the vertically moving drill string), via
the swivel into the drill string.
Circulation System
Inside the drill string (Kelly, drill pipe, drill collar) the mud
flows down to the bit where it is forced through the nozzles
to act against the bottom of the hole. From the bottom of
the well the mud rises up the annuli (drill collar, drill pipe)
and the mud line (mud return line) which is located above
the BOP. From the mud line the mud is fed to the mud
cleaning system consisting of shale shakers, settlement
tank, de-sander and de-silter. After cleaning the mud, the
circulation circle is closed when the mud returns to the mud
pit.
Circulation System
Circulation System
Circulation System
Mud Pumps
Nowadays there are two types of mud pumps in use (duplex
pump, triplex pump), both equipped with reciprocating
positive-displacement pistons. The amount of mud and the
pressure the mud pumps release the mud to the circulation
system are controlled via changing of pump liners and
pistons as well as control of the speed [stroke/minute] the
pump is moving.
Mud Pumps
Duplex Mud Pump
The duplex mud pump consists of two cylinders and is
double-acting. This means that drilling mud is pumped
with the forward and backward movement of the barrel.
Mud Pumps
Mud Pumps
Mud Pumps
Triplex Mud Pump
The triplex mud pump consists of three cylinders and is
single-acting.
Mud Pumps
Mud Pumps
The rotary System
The function of the rotary system is to transmit rotation to
the drill string and consequently rotate the bit. During
drilling operation, this rotation is to the right. The main
parts of the rotary system are:
(1)
(2)
(3)
(4)
(5)
(6)
Swivel,
Rotary hose,
Kelly,
Rotary drive (master bushing, Kelly pushing),
Rotary table and
Drill string
The rotary System
The rotary System
Swivel
The swivel which established a connection between hook
and Kelly has to be constructed extremely robust since it
has to carry the total drill string weight and at the same
time, provide a high pressure seal (connection between
flexible, non-rotating rotary hose and the rotation Kelly).
The rotary System
Kelly
The Kelly has a square or hexagonal cross-section and
provides the rotation of the drill string. Since the kelly is
made of high quality, treated steel, it is an expensive part
of the drill string. Thus to prevent the kelly from excessive
wear caused by making and breaking connections, a kelly
sub is mounted at the bottom end of it. To prevent possible
backward flow of the mud in case of an kick, a kelly cock
providing a backflow restriction valve is often mounted
between kelly and swivel.
The rotary System
Rotary Drive
The rotary drive consists of master pushing and kelly
pushing. The master pushing receives its rotational
momentum from the compound and drives the kelly
pushing which in turn transfers the rotation to the kelly
The rotary System
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