Science And Environment: How Oil Drilling Works

A brief overview of how oil drilling works, from setting up the equipment to the end of life for the well.

Oil drilling is the process of boring a hole into the earth to remove gas and oil. It is a complex operation consisting of many types of equipment. Once a site has been located, it may be leveled first to provide a stable area for the equipment. Then the site is excavated and trenched, which are very area-specific, to provide reserve and settling pits for discharges.

Rigging is then brought in and assembled. There are many rig designs for all types of drill sites. The substructure is assembled and then the rig floor is brought in. Stairways and guardrails are run for safety and access to the site. The drawworks, which is a large winch that controls the drilling line, is placed on the rig. The mast or derrick is brought in and pinned in place and pieces such as the crown section, the 'A-legs', and lines and cables are attached. Once everything is secured and laid out, the mast is raised. There are two general types of rigs used on land. An electric rig is powered by generators and engines and a mechanical rig, which is powered by engines and compound.

As part of the setting up process, crews install the circulating systems. These systems consist of mud tanks and pumps, which are large reciprocating pumps that circulate the drilling fluid. The tanks are used to allow sand and sediments to settle out of the fluid, which is then mixed with additives and reused in the pumping. The drilling fluid cools and lubricates the drill bit and removes rock fragments from the area and brings them to the surface.



Once everything has been set up and checked it is time to 'drill ahead', which means the actual drilling. Extra pipe is unloaded and readied and the pump for the drilling fluid is started. The drill bit is attached to the kelly and lowered to start drilling. As the drill goes deeper, the drilling stops and pipe is added. This continues until the desired depth is reached or oil is found. Sometimes during the drilling, a core sample is brought to the surface. This core is tested for the presence of certain markers that would indicate what is below. Sometimes drilling is deviated from vertical in order to reach a spot, this is called 'horizontal drilling'.

If the testing is favorable, the well then has casing installed and a service rig is brought in to run the production tubing down to the substance. Once this is done, a 'Christmas tree' is installed on the top. This tree is a series of control valves, pressure gauges and chokes that control the flow of oil and/or gas from the well.

While the well is being pumped, servicing the equipment takes place at regular intervals. Different setups of equipment require different scheduling and maintenance. If something goes wrong, a blowout may occur, which is an uncontrolled flow of oil, gas or other fluid.

If the well turns out to be a 'dry hole' or has reached the end of its usefulness, it is then plugged and abandoned. All equipment is removed and, if possible, salvaged. A cement plug is placed in the hole and the surface is reclaimed.

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