Main components of a drilling rig

Published: 30th January 2012
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A drilling rig mainly consists of crown block, traveling block, hook, derrick, swivel, Kelly, drawworks, rotary table, blowout preventer, bit, drill collar, drill string, centrifuge, surface casing, mud ditch, mud pit, pulsation dampener, mud pump, and engine.
1) Bit
In the final analysis, the bit is the only part of the drilling rig equipment that actually makes hole. This is not to suggest that the bit can make hole alone, nevertheless, the bit is the mast critical item of a drilling operation. To select a bit, some information must be known about the nature of the rocks to be drilled. This information always includes a factor of depth in the earth because general rock hardness (and sometimes abrasives) increases with hole depth. After selecting the bit size required, the best types of bits may be determined according to the rock formation anticipated.
2) Drill stem
Drill stem consists of three main components: drill collars, drill pipe and Kelly. The following are the principal functions of the drill stem:
① Drill stem lowers the bit into the hole and withdraws it;
② Part of the drill stem puts weigh on the bit so that the bit can penetrate the formations more effectively;
③ Drill stem transmits a turning, or rotating, action to the bit.
④ Drill stem conducts the drilling fluid under pressure from the surface to the bit.
3) Blocks and Wire Line
The traveling block, crown block and wire line are the three components whose function is to connect the supporting derrick or mast with the load of pipe to be lowered into or withdraw from the hole. As is true of almost every part of many rotary rigs, the blocks and wire-line assembly must have great strength to be able to bear heavy loads.
① Traveling block is a free moving section of a block and tackle that contains a set of pulleys or sheaves through which the drill line is threaded or revved and is opposite (and under) the crown block (the stationary section).
② A crown block is the stationary section of a block and tackle. It contains a set of pulleys or sheaves which the drill line (wire rope) is threaded or revved and is opposite and above the traveling block.
4) Derrick or mast
A mast is also called the standard mast. It is a structure with four supporting legs resting on a square base, the entire work area of the floor is in the derrick square. In contrast, the mast is much slenderer and may be thought of as sitting on one side of the derrick floor or work space. The standard derrick – except for extremely deep wells and many offshore drilling rigs – has become fairly rare today, and the mast has all put replaced it.
① Tell the features of the mast by comparing it with standard derrick
The mast has replaced the derrick for two principal reasons:
a. Derrick can be moved without being disassembled;
b. It is easy to lower when a job is finished and to erect on a new job. The standard derrick, on the other hand, has to be erected piece by piece after most moves.
② Derrick Crane is a combination of the derrick and the crane, having facility for hoisting and also for swinging the load horizontally.
5) Drawworks
A drawworks is the same general type of mechanism that is known in other industries. The two main purposes of the drawworks are:
① To lift the pipe out of the hole;
② To lower the pipe back into of the hole.
6) Blow preventer
Blowout preventer(BOP) is the equipment associated with a rig and devices installed at the wellhead to prevent fluids and gasses from unintentionally escaping from the borehole.
7) Centrifuge
Centrifuge is the equipment which is used to separate fine silt and sand from the drilling fluid.
8) Rotary table
① Introduction to rotary table
Rotary table is a mechanical device on a drilling rig. It is used to provide clockwise rotational force to facilitate the process of drilling a borehole. Rotary table is a working machine of rotating system and a critical component of drilling rig. Operating through drive bushings, the rotary rotates the Kelly and, through it, the drill stem and the bit. The Kelly drive bushing may be driven by a square opening in the rotary table or by four pins that fit into openings in the table.
② Main functions of rotary table
Rotary table serves two main functions:
a. To rotate the drill stem;
b. To hold devices called slips that support the weigh of the drill stem when the latter is not supported by hook and elevators.
9) Kelly
Kelly is 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.
10) Swivel
Swivel is a mechanical device that must simultaneously suspend the weight of the drill string, provide for rotation of the drill string beneath it while keeping the upper portion stationary, and permit high-volume flow of high-pressure drilling mud from the fixed portion to the rotating portion without leaking.
The functions of swivel are as follows:
① Support the load of the drill stem;
② Allow rotation of the drilling assembly;
③ Provide a passageway for fluid under high pressure to enter the drill stem.

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