Geology And Geophysics

How Oil Rigs Work



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An oil rig is a structured work platform located over deeply concealed fossil fuel reserves below the surface of the earth.  The equipment used is designed for boring through centuries of layered sediments, much of what is impermeable rock, or cap rock, such as granite or marble.  The men and women who operate an oil rig are well trained, often on-site for hands-on experience, and develop skills over time necessary to extract the recalcitrant crude.

After geologists have located an area where likely liquid or gaseous fossil reserves exist, on land or at sea, the process of transporting equipment to the site may require trucks barges or helicopters.  Such equipment will necessarily consists of 1) a power system which requires both diesel engines and electric powered motors; 2) Mechanical systems which would entail hoisting and turntable apparatus; 3)Rotating Equipment; 4)Casing – the large-diameter concrete pipe that lines the drill hole; 5)Circulating System; 6) Derrick – the tower or support structure that holds the drilling apparatus; and most importantly, 7)the Blowout Preventer – a valve located underground or at the sea floor that seals off or relieves pressure to the supply lines to prevent accidents similar to what occurred in the recent blowout of the BP rig in the Gulf of Mexico.

The diesel engines supply the main source of energy to power the drilling equipment and feed energy to electric motors for lighting and driving the mechanical system equipment.  The swivel, kelly and turntable make up the parts above ground that rotate the drilling apparatus.  The drilling “string” is connected sections of pipe, added as the rotating system bores into the ground.  The drill bit is at the tip of the string and eats away the cap rock and other sediment layers on its way to the location where the oil is trapped.

The drilling process would not be possible unless there was a system in place to remove the debris as the drilling bores its way through the earth and prevents overheating of parts. The elements that make up this system are the mud, mud pumps and mud pit.  The mud is a mixture of water, clay, weighting material and chemicals, used to lift rock cuttings from the drill bit to the surface. It’s made up in the mud pit by the Derrickman at or near the rig floor and transferred to the drilling string by a motorized pump.  As the drilling string makes it way to the oil or gas trap, particulate matter brought back up by the mud will alert the drilling crew they are getting close to their target.

As they progress towards this targeted area and before actually penetrating the reservoir of fossil fuel, casing pipe will be installed at intervals until rock cuttings from the mud reveal the oil sand from the reservoir rock, which is usually porous limestone or sandstone.  As they install the casing it must be reinforced with cement and capped at top and bottom.  The cement settles into the cavity outside the casing and the rock formations that have been drilled through.  The stability of this casing MUST be tested before the pressure released from penetrating an oil reservoir can be initiated.

When this process has been certified the drilling equipment will be pulled out, the capped casing will be perforated by a special perforating gun.  Small diameter tubing will be inserted where the drilling equipment was.  Control mechanisms are then set in place.  At the bottom of the tubing, on the outside circumference, a device called a “packer” is installed to help seal the casing pipe from allowing methane to escape.  Near the top, a device called a Christmas tree is put in place to control the flow of oil out into a line that sends the product to its next destination.

Provided there have been no accidents and blowout valves have been properly placed near the point where the line meets the reservoir, the reservoir rock where the oil rests, is dissolved by acid run down the tubing and out the perforated holes of the casing.  This allows the oil captured there to flow towards the well pipe.  It is at this point that the “oil rig is removed from the site and production equipment is set up to extract the oil from the well.”  This production equipment is the bobbing pump mechanism you will often see driving down a country road, especially if you’re driving through the Southwest.

Please click on the Resource links below for diagrams that offer you a better visual of this oil rig ingenuity.

 RESOURCES:

How oil drilling works

KGS – Drilling the well   



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