How Oil Drilling Works

How Oil Drilling Worksby Craig C. Freudenrich, Ph.D.In January 2001 alone, the United States produced an estimated 181 million barrels of crude oil and imported 273 million barrels from other countries. 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.

Photo courtesy Phillips Petroleum Co.Offshore oil rigHow 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.

Oil ExplorationOil is a fossil fuel that can be found in many countries around the world. In this section, we will discuss how oil is formed and how geologists find it.

Forming OilOil is formed from the remains of tiny plants and animals (plankton) that died in ancient seas between 10 million and 600 million years ago. After the organisms died, they sank into the sand and mud at the bottom of the sea.

Photo courtesy Institute of PetroleumOil forms from dead organisms in ancient seas.

Photo courtesy Institute of PetroleumClose-up of reservoir rock (oil is in black)

Over the years, the organisms decayed in the sedimentary layers. In these layers, there was little or no oxygen present. So microorganisms broke the remains into carbon-rich compounds that formed organic layers. The organic material mixed with the sediments, forming fine-grained shale, or source rock. As new sedimentary layers were deposited, they exerted intense pressure and heat on the source rock. The heat and pressure distilled the organic material into crude oil and natural gas. The oil flowed from the source rock and accumulated in thicker, more porous limestone or sandstone, called reservoir rock. Movements in the Earth trapped the oil and natural gas in the reservoir rocks between layers of impermeable rock, or cap rock, such as granite or marble.