Underground reservoirs hold oil and natural gas
Source: U.S. Energy Information Administration, U.S. Crude Oil, Natural Gas, and Natural Gas Liquids Reserves (November 2015)
A reservoir is a location where large volumes of methane, the major component of natural gas, can be trapped in the subsurface of the earth at places where suitable geological conditions occurred at the right times.
Reservoirs are made up of porous and permeable rocks that can hold significant amounts of oil and natural gas in pore spaces in the rock.
Source: U.S. Energy Information Administration, U.S. Crude Oil, Natural Gas, and Natural Gas Liquids Reserves (November 2015)
What are proved reserves?
Proved reserves of natural gas are estimated quantities that analyses of geological and engineering data have demonstrated to be economically recoverable from known reservoirs in the future.
Proved reserves are added each year with successful exploratory wells and as more is learned about fields where current wells are producing natural gas. The application of new technologies can convert previously uneconomic natural gas resources into proved reserves. U.S. proved reserves of natural gas have increased every year since 1999.
How large are U.S. proved natural gas reserves?
U.S. total natural gas proved reserves, estimated as wet gas, which includes natural gas plant liquids, set a record of nearly 389 trillion cubic feet (Tcf) in 2014. The dry gas portion of these reserves (after liquids are removed) equaled 338 Tcf. Major advances in natural gas exploration and production technologies has resulted in increased U.S. natural gas proved reserves.
What are undiscovered technically recoverable resources?
In addition to the proved natural gas reserves, there are large volumes of natural gas classified as undiscovered technically recoverable resources. Undiscovered technically recoverable resources are expected to exist because the geologic settings are favorable despite the uncertainty of their specific location. Undiscovered technically recoverable resources are also assumed to be producible over a time period using existing recovery technology. The U.S. Energy Information Administration estimated that as of January 1, 2013, the United States had 1,968 Tcf of undiscovered technically recoverable resources of dry natural gas.