Shale gas

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Shale gas is natural gas located within shale formations, which are layers of sedimentary rocks composed of silt and clay-size minerals. Shale gas is generally found throughout the United States in tight shale layers with low permeability (the ability for liquids or gases to pass through them). In 2015, U.S. production of shale gas totaled 15.2 trillion cubic feet—46 percent of total U.S. production of natural gas. This was a 65 percent increase from total U.S. shale gas production in 2010, which totaled 5.3 trillion cubic feet. According to the U.S. Energy Information Administration, the United States had 175.6 trillion cubic feet of proven shale gas reserves in 2015. Like natural gas, shale gas is used to generate electricity, heat buildings, fuel vehicles, heat water, and power furnaces in industrial facilities.

Background

Shale gas is found in unconventional reservoirs, which are layers with little capacity to transfer petroleum or natural gas through rock. On the other hand, conventional reservoirs contain oil and gas resources within interconnected spaces (similar to a sponge). This allows oil and gas to flow easily into wells for extraction at the surface.

An example of a shale gas well (click to enlarge)

In shale formations, shale gas operators must use mechanical energy to create additional outlets where the gas can be collected. One type of mechanical energy used is hydraulic fracturing (also known as fracking). The process involves injecting fluid into subterranean shale formations at high pressure. The high pressure fluid produces a fracture network that allows crude oil and natural gas inside dense rocks to flow into a wellbore and be extracted at the surface. The type of fluid used depends on the geological structure of the shale layers. In general, the fluid (known as frac fluid) contains between 98 percent and 99.5 percent water and sand; between 0.5 percent and 2 percent of the fluid is composed of chemical additives, which are used to stop the growth of microorganisms, prevent well casing corrosion, increase the rate at which the fluid is injected, and reduce pressure, among other uses.

A second type of technology to extract shale gas is horizontal drilling, which allows operators to access oil and natural gas reserves that are not directly below a drilling site. Operators drill a vertical well in the shallow section of a shale formation. Drillers then create a horizontally curved hole to access natural gas within the shale formation. Horizontal wells are used to maximize fractures so gas within shale rock can be retrieved. Horizontal drilling generally occurs alongside fracking.

Location of shale gas

The chart below shows U.S. shale gas formations according to the U.S. Department of Energy.

U.S. shale gas formations (click to enlarge)

U.S. production

Beginning in 2003-2004, operators began drilling for shale gas in the Barnett Shale in Texas. Shale gas production in the region during this period totaled approximately 2 billion cubic feet of gas per day. From 2005 to 2010, shale production in the Barnett formation totaled approximately 5 billion cubic feet of gas per day. Additionally, drillers began shale gas operations in the Marcellus Shale formation in Pennsylvania in 2003-2004 and expanded their production from 2005 to 2010.

The table below shows total U.S. shale gas production from 2010 to 2015, according to the U.S. Energy Information Administration.

Total U.S. shale gas production, 2010-2015 (in trillion cubic feet)
Year	Total shale gas production
2010	5.36
2011	7.99
2012	10.37
2013	11.41
2014	13.44
2015	15.21
Source: U.S. Energy Information Administration, "Shale Gas Production"

See also

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  Oil

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  Natural gas

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  Horizontal drilling

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  Glossary of energy terms