The United States is composed of many geologic features that have created plentiful mineral resources. One of these features is sedimentary basins, where hydrocarbon deposits are found. Sedimentary basins are located throughout the United States and contain some of the world’s largest oil and natural gas reserves.
Major Oil and Gas Reserves
There are over 70 provinces in the United States that contain hydrocarbon-bearing basins. Periodically, the U.S. Geological Survey Central Energy Team provides an assessment of hydrocarbon reserves in the United States. This information is shared with the federal government for use in the Energy Policy and Conservation Act passed in 1975. In 1995, the USGS conducted one of these assessments and discovered an additional 29 basins which contain large amounts of hydrocarbon deposits. These basins are:
- Western Oregon
- Eastern Oregon/Washington
- Sacramento Basin, CA
- San Joaquin Basin, CA
- Montana Thrust Belt
- North/Central Montana
- Eastern Great Basin
- Wyoming Thrust Belt
- Hanna, Laramie and Shirley Basin, WY
- Southwestern Wyoming
- Wind River Basin, WY
- Big Horn Basin, WY
- Powder River Basin, WY
- Bakken/Williston Basin, ND
- Uinta-Piceance Basin, CO and NM
- Denver Basin, CO
- Raton Basin, CO and NM
- San Juan Basin, CO and NM
- Permian Basin, NM and TX
- Fort Worth Basin, TX and OK
- Arkoma Basin, AR and OK
- Michigan Basin
- Illionois Basin
- Black Warrior Basin, MS and AL
- Gulf Coast Region
- Appalachian Basin
- Florida Peninsula
- Northern Alaska
- Central Alaska
Many of these hydrocarbon reserves, such as the Bakken/Williston Basin and the Gulf Coast Region, are currently being exploited for their oil, natural gas and coal deposits. However, many more of these reserves, such as those throughout the Rocky Mountain region in Colorado and Wyoming, are not yet being tapped for their resources. This could be due to the high cost of excavation compared to the amount of hydrocarbons expected to be found. Another major reason is the negative environmental impact that could be caused by excavation.
The Geology of Hydrocarbon Reserves in the United States
Hydrocarbon forms in sedimentary environments, where organic material has been buried under multiple layers of sedimentary material. At one point or another during North America's geolgical evolution, large portions of the continent were buried under a marine environment. Today, hydrocarbon reserves are found deep below the surface, withing limestone, sandstone and shale deposits. Limestone, sandstone and shale deposits indicate an ancient marine environment and provide further proof that the North American continent was once at the bottom of a sea during a time when sea-levels were much higher than they are today.
The first stage in natural gas, oil and coal exploration is to seek out these types of geological areas, where sedimentary deposits may hold a large hydrocarbon reserve. Geologists conduct above-surface field testing of these areas which rely mainly on acoustical techniques that can "hear" into the ground. Areas where a hydrocarbon pocket exists will "sound" differently than areas that are solid rock all the way down. These techniques were used by the USGS Central Energy Team for their assessment in 1995. The next stage is for an exploration company or mining company to survey the area and determine if the cost associated with excavating the hydrocarbons is worth the amount of mineral resources present.
Sources:
USGS National Oil and Gas Assessment, usgs.gov
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Alexandra Matiella Novak - With a PhD in Geology and expertise in science education, Alexandra is passionate about increasing the public's Earth science literacy.
