How Oil Drilling Works?

In 2008 alone, the United States produced an estimated 4.9 million barrels of crude oil per day and imported 9.8 million barrels per day from other countries [source: U.S. Energy Information Administration]. This oil gets refined into gasoline, kerosene, heating oil and other products. To keep up with our consumption, oil companies must constantly look for new sources of petroleum, as well as improve the production of existing wells.

Oil Rig Systems

Anatomy of an oil rig

Once the equipment is at the site, the crew sets the rig up. Here are the major systems of a land oil rig:

• Power system
• large diesel engines - burn diesel-fuel oil to provide the main source of power
• electrical generators - powered by the diesel enginesto provide electrical power
• Mechanical system - driven by electric motors
• hoisting system - used for lifting heavy loads; consists of a mechanical winch (drawworks) with a large steel cable spool, a block-and-tackle pulley and a receiving storage reel for the cable
• turntable - part of the drilling apparatus
• Rotating equipment - used for rotary drilling
• swivel - large handle that holds the weight of the drill string; allows the string to rotate and makes a pressure-tight seal on the hole
• kelly - four- or six-sided pipe that transfers rotary motion to the turntable and drill string
• turntable or rotary table - drives the rotating motion using power from electric motors
• drill string - consists of drill pipe (connected sections of about 30 feet (10 meters) and drill collars (larger diameter, heavier pipe that fits around the drill pipe and places weight on the drill bit)
• drill bit(s) - end of the drill that actually cuts up the rock; comes in many shapes and materials (tungsten carbide steel, diamond) that are specialized for various drilling tasks and rock formations
• Casing - large-diameter concrete pipe that lines the drill hole, prevents the hole from collapsing, and allows drilling mud to circulate
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  Photo courtesy the Energy Institute
  Mud circulation in the hole
  Circulation system - pumps drilling mud (mixture of water, clay, weighting material and chemicals, used to lift rock cuttings from the drill bit to the surface) under pressure through the kelly, rotary table, drill pipes and drill collars
  • pump - sucks mud from the mud pits and pumps it to the drilling apparatus
  • pipes and hoses - connects pump to drilling apparatus
  • mud-return line - returns mud from the hole
  • shale shaker - shaker/sieve that separates rock cuttings from the mud
  • shale slide - conveys cuttings to the reserve pit
  • reserve pit - collects rock cuttings separated from the mud
  • mud pits - where drilling mud is mixed and recycled
  • mud-mixing hopper - where new mud is mixed and then sent to the mud pits
• Derrick - support structure that holds the drilling apparatus; tall enough to allow new sections of drill pipe to be added to the drilling apparatus as drilling progresses
• Blowout preventer - high-pressure valves (located under the land rig or on the sea floor) that seal the high-pressure drill lines and relieve pressure when necessary to prevent a blowout (uncontrolled gush of gas or oil to the surface, often associated with fire)

Oil Drilling Preparation

Once the site has been selected, scientists survey the area to determine its boundaries, and conduct environmental impact studies if necessary. The oil company may need lease agreements, titles and right-of way accesses before drilling the land. For off-shore sites, legal jurisdiction must be determined.

After the legal issues are settled, the crew goes about preparing the land:

1. The land must be cleared and leveled, and access roads may be built.
2. Because water is used in drilling, there must be a source of water nearby. If there is no natural source, the crew drills a water well.
3. The crew digs a reserve pit, which is used to dispose of rock cuttings and drilling mud during the drilling process, and lines it with plastic to protect the environment. If the site is an ecologically sensitive area, such as a marsh or wilderness, then the cuttings and mud must be disposed of offsite -- trucked away instead of placed in a pit.

Once the land has been prepared, the crew digs several holes to make way for the rig and the main hole. A rectangular pit called a cellar is dug around the location of the actual drilling hole. The cellar provides a work space around the hole for the workers and drilling accessories. The crew then begins drilling the main hole, often with a small drill truck rather than the main rig. The first part of the hole is larger and shallower than the main portion, and is lined with a large-diameter conductor pipe. The crew digs additional holes off to the side to temporarily store equipment -- when these holes are finished, the rig equipment can be brought in and set up.

Depending upon the remoteness of the drill site and its access, it may be necessary to bring in equipment by truck, helicopter or barge. Some rigs are built on ships or barges for work on inland water where there is no foundation to support a rig (as in marshes or lakes).

In the next section, we'll look at the major systems of an oil rig.k for new sources of petroleum, as well as improve the production of existing wells.
How does a company go about finding oil and pumping it from the ground? You may have seen images of black crude oil gushing out of the ground, or seen an oil well in movies and television shows like "Giant," "Oklahoma Crude," "Armageddon" and "Beverly Hillbillies." But modern oil production is quite different from the way it's portrayed in the movies.

In this article, we'll examine how modern oil exploration and drilling works. We'll discuss how oil is formed, found and extracted from the ground.

Oil is a fossil fuel found in many countries around the world. On the next page, we'll discuss how oil is formed and how geologists find it.

The Oil Drilling Process

Photo courtesy ConocoPhillips
Rotary workers trip drill pipe.

The crew sets up the rig and starts the drilling operations. First, from the starter hole, the team drills a surface hole down to a pre-set depth, which is somewhere above where they think the oil trap is located. There are five basic steps to drilling the surface hole:

1. Place the drill bit, collar and drill pipe in the hole.
2. Attach the kelly and turntable, and begin drilling.
3. As drilling progresses, circulate mud through the pipe and out of the bit to float the rock cuttings out of the hole.
4. Add new sections (joints) of drill pipes as the hole gets deeper.
5. Remove (trip out) the drill pipe, collar and bit when the pre-set depth (anywhere from a few hundred to a couple-thousand feet) is reached.

Once they reach the pre-set depth, they must run and cement the casing -- place casing-pipe sections into the hole to prevent it from collapsing in on itself. The casing pipe has spacers around the outside to keep it centered in the hole.

New Drilling Technologies The U.S. Department of Energy and the oil industry are working on new ways to drill oil, including horizontal drilling techniques, to reach oil under ecologically-sensitive areas, and using lasers to drill oil wells.

The casing crew puts the casing pipe in the hole. The cement crew pumps cement down the casing pipe using a bottom plug, a cement slurry, a top plug and drill mud. The pressure from the drill mud causes the cement slurry to move through the casing and fill the space between the outside of the casing and the hole. Finally, the cement is allowed to harden and then tested for such properties as hardness, alignment and a proper seal.

In the next section we'll find out what happens once the drill bit reaches the final depth.