Oil and Gas Resources in the United States
Commercially viable quantities of oil and gas are found in many parts of the United States.
Where Are Oil and Gas Resources Found?
Oil and natural gas deposits are located in sedimentary rocks. Common hydrocarbon-containing structures are those in which a relatively porous rock has an overlying low-permeability rock that would trap the hydrocarbon. Common structural traps are anticlines (upward folds in the rock layers) and faults (fractures in the earth's surface where layers are shifted).
While the source rock for conventional natural gas is usually different than the reservoir rock, for coal bed methane the coal seam serves as both the source rock and the reservoir rock. Coal bed methane is trapped within coal seams and held in place by hydraulic pressure. Coal bed methane is retained in a coal seam in one of three ways:
Coal bed methane can also be found as adsorbed gas in strata (conventional reservoirs) adjacent to the coal bed. Coal can store six to seven times more gas than an equivalent volume of rock common to conventional gas reservoirs. Coal mine methane, a sub-category of coal bed methane, is gas trapped in areas that are expected to be mined, while most coal bed methane occurs in seams that are not economical to mine.
For shale gas formations, the source rock also serves as the reservoir rock. Shale gas is typically a dry gas, but some formations can produce water and gas. Shale is a sedimentary rock that is comprised of clay-sized particles that have been consolidated over time. The plate-like clay particles were deposited with organic matter like algae and plants. Because the plate-like clay particles are very small and tended to lie flat when they were deposited, gas shale formations tend to have limited permeability horizontally and almost no permeability vertically. Natural gas contained in the shale cannot move easily because it is trapped within the formation. However, several factors have come together to make shale gas production important: 1) the wide distribution of highly organic shales containing vast resources of natural gas, 2)advances in horizontal drilling, 3) advances in hydraulic fracturing, and 4) increases in natural gas prices.
Where in the United States Are Oil and Gas Resources Concentrated Enough for Commercial Production?
Within the United States, crude oil is produced in 31 states and off the coasts of Alaska, California, Louisiana, and Texas. The top crude oil producing states are Texas, Alaska, California, Louisiana, and Oklahoma. About one-fourth of the crude oil produced in the U.S. is produced offshore in the Gulf of Mexico. Over the last several decades, the amount of domestically produced crude oil has been decreasing while the use of products made from crude oil has been increasing. About 58% of crude oil and petroleum products are imported.
Natural gas is found in 33 states. In 2006, the U.S.-marketed production of natural gas was 19.4 trillion cubic ft (Tcf). The top natural gas-producing states were Texas (5.5 Tcf), Wyoming (1.8 Tcf), Oklahoma (1.7 Tcf), New Mexico (1.6 Tcf), Louisiana (1.4 Tcf), and Colorado (1.2 Tcf).
Historical U.S. oil and natural gas production is shown in the United States Geological Survey (USGS) map above. The USGS has also produced a short video clip of U.S. oil and gas exploration and production from 1900 through 2005.
Where in the United States are coal bed methane resources concentrated enough for commercial production?
About 13% of land in the lower 48 states has some coal under it, and all coal deposits have methane and water as a byproduct of the coal formation process (coalification). The bulk of U.S. coal bed methane (CBM) resources are located in 13 major basins. About 56% of the production has come from the Rocky Mountains.
The most active areas of commercial CBM production are the Black Warrior Basin (Alabama/Mississippi), San Juan Basin (Southern Colorado/northern New Mexico), and Powder River Basin (Wyoming/Montana). Production is starting to increase in the Piceance Basin of Colorado, which is estimated to contain about one-quarter of the U.S. coal CBM resources. While the San Juan Basin is the major CBM field in terms of daily production, it is at or near its maximum production. The Powder River Basin, the Raton Basin (northern New Mexico), and the Uinta Basin (Utah) are also becoming major CBM fields. Major CBM production areas are shown on the map to the right.
About 100 trillion cubic feet of coal bed methane are economically recoverable in the United States (a five-year supply at present rates of recovery).
Where in the United States are shale gas resources concentrated enough for commercial production?
Shale gas formations are present in multiple Rocky Mountain and Appalachian Mountain states, the Dakotas, Kansas, Nebraska, Texas, Oklahoma, Arkansas, Louisiana, Illinois, Indiana, Kentucky, Ohio, and Wisconsin. Shale formations experiencing the most activity (in terms of either exploration or production) are the Barnett Shale, the Haynesville/Bossier Shale, the Antrim Shale, the Fayetteville Shale, the Marcellus Shale and the New Albany Shale. Analysts have estimated that most new reserves growth will come from the shale gas reservoirs. The total recoverable gas resources from just 4 of the shale gas formations (Haynesville, Fayetteville, Marcellus and Woodford) may be over 550 TCF, a relatively significant reserve considering the U.S. consumes about 23 TCF/year of natural gas.