 PetroStrategies, Inc. |
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Drilling Operations TopicsHow 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
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 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
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 SystemThe 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 SystemA 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.
Drilling GeometriesWells can be drilled in a number of different geometries from the simplest vertical well to complicated multilateral completions. Directional drilling technology allows the industry to access deposits that would otherwise be inaccessible.
The Rig Crew
The toolpusher, the location supervisor for the drilling contractor, is usually a senior, experienced individual who has worked his way up through the ranks of the drilling crew positions. His job is largely administrative, including ensuring that the rig has sufficient materials, spare parts and skilled personnel to continue efficient operations.
The driller
is the supervisor of the rig crew. The driller is responsible for the
efficient operation of the rigsite as well as the safety of the crew.
He typically has many years of rigsite experience and has worked his
way up from other jobs. While the driller must know how to perform
each of the jobs on the rig, his or her role is to supervise the work
and control the major rig systems. The driller operates the pumps,
drawworks, and rotary table via the drillers console-a control room of
gauges, control levers, rheostats, and other pneumatic, hydraulic and
electronic instrumentation. The driller also operates the drawworks
brake using a long-handled lever. Hence, the driller is sometimes
referred to as the person who is "on the brake.“
The motorman is responsible for maintenance of the engines. While all members of the rig crew help with major repairs, the motorman does routine preventive maintenance and minor repairs. A roughneck is a low-ranking member of the drilling crew. The roughneck usually performs semiskilled and unskilled manual labor that requires continual hard work in difficult conditions for many hours. After roughnecks understand how the rig operates and demonstrates their work ethic, they may be promoted to other positions in the crew. A roustabout is any unskilled manual laborer on the rigsite. A roustabout may be part of the drilling contractor's employee workforce, or may be on location temporarily for special operations. Roustabouts are commonly hired to do the peripheral tasks, ranging from cleaning up location to cleaning threads to digging trenches to scraping and painting rig components.
Drilling CostsThe drilling company operates in accordance with a contract which specifies that the well will be drilled to a specific depth. The contractor is paid on a per day or per foot drilling rate. In 2006 it cost $2.238 million to drill an oil well and $1.936 million to drill a natural gas well. The average cost to drill a well was $324/foot of depth.
The
average cost to find and develop an oil and gas property in the United
States was $17.01/BOE from 2005-2007. The cost for onshore
development was $13.38/BOE and for offshore development was $49.54/BOE. BOE is the barrels of oil equivalent.
Drilling costs have increased as oil prices have and drilling activity have risen. In 2000, when oil prices were $26.72 /B, drilling costs were $593 thousand per oil well and $126/foot. For 2006, when prices averaged $59.69/B, drilling costs were $2.238 million per oil well and $402/foot.
Drilling activity is reported in terms of the number of drilling rigs operating and the number of wells drilled. PetroStrategies reports these values in two graphs Rig Count and Wells Drilled.
Copyright
2000 |
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