How Natural Gas Is Formed

The United States is endowed with substantial natural gas resources, and new discoveries and advances in drilling techniques have revised estimates of their size sharply upward in the past few years. In 2009, the U.S. Energy Information Administration (EIA) estimated that the U.S. possesses 2,203 trillion cubic feet of natural gas that could be recovered using current technology.

Conventional resources represent 46 percent (1,009 trillion cubic feet) of the total resource base, while the rest includes unconventional natural gas resources, such as tight gas, shale gas, and coalbed methane. Of the total U.S. gas resource, 273 trillion cubic feet of gas are classified as “reserves,” which can be extracted under current economic and operational conditions [1].

As of 2012, the largest known gas reserves in the world are found in Russia, which has five times the reserves of the United States [2]. Iran and Qatar have four and three times as much gas as the U.S., respectively, and significant reserves are also present in Saudi Arabia, Turkmenistan, United Arab Emirates, Nigeria, and Venezuela. Total world reserves of natural gas are estimated at 6,707 trillion cubic feet [3].

Exploration and production of conventional natural gas resourcesPotential natural gas deposits can be located with seismic testing methods similar to those used for petroleum exploration. In such tests, gas prospectors use seismic trucks or more advanced three-dimensional tools that involve setting off a series of small charges near the Earth’s surface to generate seismic waves thousands of feet below ground in underlying rock formations.

By measuring the travel times of these waves through the Earth at acoustic receivers known as "geophones," geophysicists can construct a picture of the subsurface structure and identify potential gas deposits. However, to verify whether the rock formation actually contains economically recoverable quantities of natural gas or other hydrocarbons, an exploratory well must be drilled.

Once the viability of a site is determined, vertical wells are drilled to penetrate the overlying impermeable cap rock and reach the reservoir. Natural buoyancy then brings the gas to the surface, where it can be processed and sent to homes.