Petroleum companies extract crude oil from the Earth using a perforation in the Earth's surface called an oil well. Crude oil is a liquid form of petroleum. In addition, wells provide natural gas. Refining crude oil produces gasoline, diesel fuel and other useful petroleum products.
Oil wells are 5 to 36 inches in diameter. The drill bit breaks through the ground and drilling fluid brings the particles to the surface. The drillers add casing or pipe to provide structural integrity to continue drilling through formations that are less stable. As fluid returns to the surface, the drillers strain it to remove the rock cuttings and fluid recycles into the well to remove more cuttings. Completing the well includes adding perforated casing in the production zone for the oil to flow into the well. Once the well is complete, the crew removes the drilling rig and installs a pump. The pump removes the oil and distributes it to a network for transportation to the refinery. As a well reaches the point where it is no longer economically sound to operate, the operator pours cement into certain parts of the casing to prevent intermixing of gas and oil. The company installs a cap and buries the well.