How is crude oil found and produced?
Geologists preparing a hole for the explosive charges used in seismic exploration
Schematic of different types of oil and natural gas wells
Schematic of the basic types of oil and natural gas deposits
The search for crude oil begins with geologists who study the structure and history of rock layers below the earth's surface to locate areas that may contain deposits of oil and natural gas.
Geologists often use seismic surveys on land and in the ocean to find the right places to drill wells. Seismic surveys on land use echoes from a vibration source at the surface of the earth, usually a vibrating pad under a special type of truck. Geologists can also use small amounts of explosives as a vibration source. Seismic surveys conducted in the ocean rely on blasts of sound that are used to create sonic waves to explore the geology beneath the ocean floor.
If a site seems promising, an exploratory well is drilled and tested. When an economical amount of oil is found, development wells are drilled. Different types of wells are drilled depending on the location, geology, and oil resource.
Advances in drilling and production technologies have increased U.S. oil production
Advances in drilling and production technologies and the application of those technologies has led to increases in U.S. oil and natural gas production. In the past, a drilling rig drilled a single vertical well. Now many directional or horizontal wells can be drilled from one location or well pad to access greater areas of oil and natural gas bearing rock.
Oil may flow to the surface from natural pressure in the rock formation or it may be forced out of the ground and up through the well depending on the type of reservoir in which it is located. In situations where oil needs to be forced out of the ground, various technologies are used to enable the flow of oil and natural gas from the reservoir or resource bearing rock into the wells.
Hydraulic fracturing is used to access oil and natural gas contained in tiny pores of geological formations composed of shale, sandstone, and carbonate (limestone) rock. Hydraulic fracturing breaks up the rock in the formations and creates pathways that allow oil and natural gas to escape rock layers. Hydraulic fracturing involves forcing water, chemicals, and sand or other proppants (materials used to keep the pathways open) under high pressure into wells. Steam, water, or carbon dioxide (CO2) can also be injected into a rock layer to help oil flow more easily into production wells.
Once the oil has been collected from wells in a production field, the oil is transported by pipelines, trucks, or trains to refineries, or it may be taken to a port and loaded on ships for transport to other countries.
Conventional and unconventional production
Production of crude oil and natural gas is sometimes categorized as conventional production or unconventional production. Conventional production generally means that crude oil and natural gas flow to and up a well under the natural pressure of the earth. Unconventional production requires techniques and technologies to increase or enable oil and natural gas production beyond what might occur using conventional production techniques. In the United States, most of the new oil and natural gas production activities on land use unconventional production technologies.