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How Do Engineers Drill for Oil and Gas?

 

It is necessary to drill a hole to obtain crude oil and natural gas from under the earth's surface. Engineers make this hole using a rotary drilling rig.

The Rotary Drilling Rig

The rotary drilling rig uses a drill bit to cut through the earth and create a hole. As the hole gets deeper, pipe is added to the drill bit to allow it to dig further. These lengths of drill pipe form the drill string. This pipe is connected to an engine that turns the drill bit to cut the hole. The rotary rig operates the same as a hand-held electric drill. The electric drill has a motor that turns the drill bit and sufficient weight must be applied to keep the drill in contact with the bottom of the hole.   

 

 

 

 

There are four main operations in a drilling rig: hoisting, rotating, circulating, and power. The hoisting system is used to raise and lower pipe in and out of the hole and to support the drill string to control the weight on the drill bit during drilling.

Hoisting System

The hoisting system consists of the derrick, traveling and crown blocks, the drilling line, and the drawworks. The drilling rig uses a derrick to support the drill bit and pipe (drill string). The derrick is a steel tower that is used to support the traveling and crown blocks and the drill string. There may be no more identifiable symbol of the oil and gas industry than the derrick on a drilling rig. 

The crown and traveling blocks are a set of pulleys that raise and lower the drill string. The crown block is a stationary pulley located at the top of the derrick. The traveling block moves up and down and is used to raise and lower the drill string. These pulleys are connected to the drill string with a large diameter steel cable.

The cable is connected to a winch or drawworks. The drawworks contains a large drum around which the drilling cable is wrapped. As the drum rotates one way or the other, the drilling cable spools on or off the drum and raises or lowers the drill string.

Rotating Equipment

The rotating equipment turns the drilling bit. This equipment consists of the swivel, the kelly, the rotary table, the drill pipe, the drill collars, and the bit. The swivel is attached to the bottom of the traveling block and permits the drill string to rotate. The kelly is a square or hexagonal shaped section of pipe that is attached to the swivel. The kelly fits in a matching slot in the rotary table. As the rotary table turns the kelly is also turned. The movement of the kelly rotates the drill string and the drill bit.

Drilling pipe is round steel tubes about 30 feet long with a diameter of from 4 to 5 inches. The drill collars are used to add weight on the bit. Drill pipe has threaded connections on each end that allow the pipe to be joined together to form longer sections as the hole gets deeper.

The drilling bit is used to create the hole. Drilling bit sizes range from six inches to three feet in diameter. The most common drill bits are roller cone bits and diamond bits. Roller cone bits have three cones containing rows of teeth. The cones rotate on bearings and turn as the drilling bit rotates. 

The teeth cut and crush the rock to create the hole. The bit also contains small nozzles that spray drilling fluids to remove the rock fragments from the bottom of the hole. 

Diamond bits have a single fixed head that contains many small diamonds. As the bit turns the diamonds cut the rock. Diamond bits also have nozzles to wash away the broken pieces of rock. Different drilling bits are used depending on the type of rock that is encountered.

Circulating System

The drilling operation uses fluids to reduce friction and remove rock fragments or cuttings. The circulating system pumps these drilling fluids down the hole, out of the nozzles in the drilling bit, and returns them to the surface where the debris is separated from the fluid.

Drilling fluid is also knows as drilling mud because of its characteristic brown color. The drilling mud is mixed in tanks. The mud is pumped through a hose to the swivel, down the kelly, and into the drill pipe. The mud goes down the drill string and out of the drilling bit nozzles. The mud carries the cuttings from the bottom of the hole to the surface in the space between the outside of the drill string and the inside of the hole.

The cuttings are separated from the mud in a vibrating screen called a shale shaker. The cuttings are trapped on the screen and the mud passes through the screen into the mud pits. The circulating pumps pick up this clean mud and send it back down the hole. The cuttings are collected in a plastic-lined pit for disposal.

Drilling mud is a mixture of water, clay, and special minerals and chemicals. Drilling mud removes cuttings from the hole and cools and lubricates the drilling bit. Mud also maintains pressure in the hole to keep fluids in the formation from entering the hole and producing a gusher of oil on the surface. Different muds are used during the drilling process to adjust to rock formations, temperature, and pressure.

Power System

A drilling rig needs power to operate the circulating, rotating, and hoisting systems. This power comes from two or more diesel engines. Power is transmitted to the drilling rig from either generators that provide electricity or mechanical drivers that use a series of pulleys and belts to transmit power from the engines to the components that require the power.

The Rig Crew

 

Drilling is usually done by a service company or drilling contractor. The drilling crew is composed of a toolpusher, a driller, a derrickhand, and several roughnecks. The toolpusher manages the drilling operation. The driller operates the rig. The derrickhand helps with the drilling mud and in removing pipe from the hole. Roughnecks help with the drilling operation and maintaining the drilling equipment.

 








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