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

Rotary Drilling Rig

Land rigs:Conventional rigs:

Small land rigs,Medium land rigs,Large land rigs,

Mobile rigs:Portable mast,Jacknife,

In general, rotary rigs can be distinguishedinto:

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.

In general, rotary rigs can be distinguished into:

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].

Rig Power 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

Hoisting System

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

Draw works

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

Circulation System

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

Mud Pumps

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) Swivel, (2) Rotary hose, (3) Kelly, (4) Rotary drive (master bushing, Kelly pushing),(5) Rotary table and (6) 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

The rotary System

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