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Learn more about natural gas and related industry terminology with the glossary below.

The American Gas Association and U.S. Department of Energy also provide comprehensive alphabetized lists of industry terminology for reference.


Ardmore Basin

The Ardmore Basin extends across Bryan, Carter, Johnston, Love and Marshall Counties in Oklahoma and includes the Woodford Shale.


An underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, or silt) from which groundwater can be usefully extracted using a water well.


Bakken Formation

The Bakken is a geological formation occupying about 200,000 square miles of the subsurface of the Williston Basin. It straddles the U.S. border with Canada and runs through two states, Montana and North Dakota, as well as two Canadian provinces, Saskatchewan and Manitoba.

Barnett Shale

The Barnett is a geological formation located in the Bend Arch-Fort Worth Basin in Texas. It consists of sedimentary rocks, and the productive part of the formation is estimated to stretch from the city of Dallas west and south, covering 5,000 square miles (13,000 square km) and at least 18 counties.


Carbon Capture & Storage

Carbon Capture and Storage (CCS) is a combination of existing technologies, with the potential to play a major role in the management and reduction of global carbon dioxide (CO2) levels. The CCS process allows for CO2 emissions released during energy production to be captured and stored underground.

Conventional gas

Conventional gas is natural gas that is produced by a well drilled into a geologic formation in which the reservoir and fluid characteristics permit the natural gas to flow readily to the wellbore.

Cotton Valley Formation

The Cotton Valley Formation natural gas field is located above the Haynesville Shale in East Texas and North Louisiana. The field extends from about 7,800 - 10,000 feet deep and is made up of shale, sandstone and clay deposits that contain natural gas.


Duvernay Shale

The Duvernay Shale is located in remote areas of Western Canada, and is estimated to contain more than 440 trillion cubic feet of natural gas and more than 60 billion barrels of oil.


Eagle Ford Shale

The Eagle Ford shale is located in South Texas, and is one of the most active shale plays in the world. The origin behind the name of the play is derived from the town of Eagle Ford, Texas, where the shale outcrops at the surface in a clay form.

Energy security

A term used to refer to the reliability of future energy supply. This depends on a number of different factors, including the availability of energy supplies, their affordability, and the capacity to extract them in an environmentally sustainable manner.

Evaporation ponds

Artificial ponds with large surface areas that are designed to allow the efficient evaporation of water through exposure to sunlight and ambient surface temperatures.

Extraction process

The method used for drawing out resources from the ground. For unconventional gas, this is mainly hydraulic fracturing.


Fayetteville Shale

The Fayetteville Shale, part of the Arkoma Basin in Arkansas, is a 50-mile-wide formation stretching across Central Arkansas.

Flowback water

During unconventional gas development, typically 10 to 70 percent of the water used is recoverable in the first two to three weeks, depending on the geology of the shale formation. Flowback water is then separated from the natural gas. Such recovered water may contain suspended clay particles, dissolved inorganic components, organic compounds from the fracturing fluid, and/or sand and silt particles from the shale or proppant.


See “Hydraulic fracturing”.


The Fontenelle is a natural gas field located in Wyoming.

Free gas

Natural gas that is trapped within spaces in the rock, making it more accessible.


The Freestone Trend is a production area located in the western shelf of the East Texas Basin in Freestone and other counties in Texas.


Haynesville Shale / Bossier Shale

The Haynesville Shale play is located in northwestern Louisiana, East Texas and the southwestern tip of Arkansas. The play was discovered in 2008 and has generated a vast amount of interest and activity. The Bossier Shale, located just above the Haynesville, has also sparked success. The area is commonly referred to as the Haynesville/Bossier Shale, but they are independent producing developments.

Horizontal drilling

A hydrocarbon well drilling technique that allows for multiple underground wellbores to be drilled from one surface well site.


The Hugoton gas field is a large natural gas field stretching across Kansas, Oklahoma and the Texas Panhandle.

Hydraulic fracturing

A process through which small fractures are made in impermeable rock by a pressurized combination of water, sand and chemical additives. The small fractures are held open by grains of sand, allowing the natural gas to flow out of the rock and into the wellbore.


An organic compound (as acetylene or butane) containing only carbon and hydrogen and often occurring in petroleum, natural gas, coal and bitumens.


Induced seismicity

Earthquakes attributable to human activities are called "induced seismic events" or "induced earthquakes." Globally, the vast majority of earthquakes that occur have natural causes. Under unique circumstances, some of these earthquakes can be related to human activities. In these rare instances, the induced seismicity is caused by man-made changes to reservoir pressure or stress, in the presence of an unstable fault and a critical stress state in the rocks.

Generally, seismic events with a magnitude (M) greater than 2.0 have the possibility of being felt, particularly if they occur at shallow depths, but smaller seismic events (M<2.0) generally are not felt.


Liquefied Natural Gas (LNG)

Liquefied Natural Gas is natural gas that has been cooled to -162 °C to convert the gas temporarily to a liquid state for storage or transportation purposes. As a liquid, natural gas occupies about 600 times less space than when in its gaseous form. LNG is principally used for transporting natural gas to distant markets, where it is re-gasified and distributed via pipelines to consumers.


Marcellus Shale

Stretching from parts of New York, Pennsylvania, West Virginia and Ohio, the Marcellus Shale is one of the first shale plays to be tapped, after the Barnett Shale in Texas, and has become one of the world’s largest natural gas fields.

Monterey Shale

The Monterey Shale is located in Northern California and extends south toward Los Angeles and offshore.


A unit of measure for permeability.


Natural Gas Liquids (NGLs)

A liquid fuel produced in association with natural gas. NGLs are components of natural gas that are separated from the gaseous state into liquid form during natural gas processing.



Permeability is the measure of how natural gas or other fluids move through the rock (typically measured in "millidarcies").

Permian Basin

The Permian Basin is a significant oil-and-gas-producing region located in West Texas and southeastern New Mexico with various producing formations.


Porosity measures the open space ("pore space") between grains. The lower the porosity, the more important hydraulic fracturing is to extracting natural gas.


Ratón Basin

The Ratón Basin, derived from the Ratón Pass in Ratón, New Mexico, is located in southern Colorado and northern New Mexico. It is mainly comprised of coalbed methane and coal.


Natural gas or oil reserves are defined as technically recoverable resources (see below). This means that the reserves can be extracted from the ground using current technologies; however it does not guarantee that this extraction process can be achieved in an economically viable manner.


A naturally occurring storage area below the earth's surface, essentially a "folded" rock formation that traps and holds natural gas or oil. The reservoir rock must be permeable and porous to contain the hydrocarbons, and it has to be capped by relatively impermeable rock layers in order to form an effective seal and prevent the hydrocarbons from escaping. Reservoirs are routinely described as either "conventional" or "unconventional."

Typical conventional reservoir rocks are sedimentary and include sands, sandstones, arkoses, and fissured limestone and dolomite. Also of interest are reservoirs commonly referred to as "unconventional,” including shale reservoirs, tight sandstone reservoirs, coal bed methane reservoirs and tight oil reservoirs. The main difference between conventional and unconventional reservoirs is that unconventional resources require some form of stimulation to produce commercial volumes of hydrocarbon.

Further, unconventional gas resources are generally not buoyancy-driven accumulations and are regionally pervasive accumulations, most commonly independent of structural and stratigraphic traps. In unconventional gas and tight oil reservoirs, the main challenge is to improve the permeability of the rock through which the hydrocarbons flow. This is done through hydraulic fracturing, which creates fissures in the rock to increase its permeability, releasing the hydrocarbons from the pores in which they are trapped, and allowing the hydrocarbons to flow to the well.


San Juan Basin

The San Juan Basin extends from northwest New Mexico into southwest Colorado, and is one of the oldest producing areas in the United States. The basin primarily produces natural gas, but crude oil production is increasing in the region.

Sedimentary rock

Sedimentary rock is one of the three main rock groups (along with igneous and metamorphic rocks) and is formed in these ways: by the deposits of the weathered remains of other rocks; by the deposits of the results of biogenic activity; and by precipitation. Sedimentary rocks include common types such as chalk, limestone, sandstone and shale.

Shale basins

The underground rock formations that serve both as natural gas generators and reservoirs.


Slickwater fracturing is a method or system of hydraulic fracturing that involves adding chemicals to water to increase the fluid flow. Slickwater increases the speed at which the pressurized fluid can be pumped into the wellbore.

Surface footprint

The ground space utilized to undertake industrial operations, including natural gas extraction.


Tight gas

Like shale gas and coal bed methane, tight gas is a type of unconventional gas produced from reservoir rocks with low permeability (having less than 0.1 millidarcy (mD) of permeability and less than 10 percent matrix porosity) and requires hydraulic fracturing to extract and economically produce.


Uinta Basin

Located in Northeast Utah, the Uinta Basin was developed in commercial volumes in 1925. Like the Permian Basin, the Uinta Basin has rapidly increased in production over the years.

Unconventional gas

An umbrella term for natural gas that is produced by means that do not meet the criteria for conventional production. See "conventional gas” above. Note: What is qualified as "unconventional" at any particular time is a complex interactive function of resource characteristics, the available exploration and production technologies, the current economic environment, and the scale, frequency and duration of production from the resource. Perceptions of these factors inevitably change over time and they often differ among users of the term.


A few thousand feet below the Marcellus Shale, the Utica Shale has large amounts of natural gas, natural gas liquids and crude oil in eastern Ohio and western Pennsylvania. Scientists consider the Utica Shale to be a natural gas and oil source rock, where the natural gas and oil generated is produced from reservoirs in overlying rock units.



The channel created by the drill bit.