This glossary includes many of the common words and phrases used by the natural gas industry.
CF: One cubic foot of natural gas
MCF: One thousand cubic feet of natural gas
MMCF: One million cubic feet of natural gas
BCF: One billion cubic feet of natural gas
TCF: One trillion cubic feet of natural gas
MMCFD: Millions of cubic feet of gas per day
BOE: Barrel of oil equivalent (one barrel of oil = 6,000 cubic feet of natural gas)
MBOE: One thousand barrels of oil equivalent
MMBOE: One million barrels of oil equivalent
Definition of Terms
Coalbed methane (CBM): Natural gas extracted from coal beds.
Conventional natural gas: The bulk of the United States' current gas production comes from what is termed conventional gas reservoirs, which are typically underground sandstone or carbonate formations with moderate to high permeability.
Department of Energy (DOE): A United States cabinet-level federal agency responsible for managing national energy policy, nuclear power, nuclear weapons programs and the national energy research labs.
Directional drilling: The application of special tools and techniques to drill a wellbore at a predetermined angle. Horizontal drilling is a form of directional drilling where the wellbore is ultimately drilled at +/- 90 degrees to the vertical direction.
Dry gas: Also called consumer-grade natural gas, dry gas is almost pure methane and occurs in the absence of condensate or liquid hydrocarbons or by processing natural gas to remove liquid hydrocarbons and impurities.
Energy Information Administration (EIA): An agency within the U.S. Department of Energy. EIA provides energy data, forecasts and analyses. www.eia.gov
Field: A geographical area in which a number of oil or gas wells produce from a continuous reservoir. A field may refer to surface area only or to underground productive formations.
Flowback fluids: The fluids flowed back or recovered from a well that were injected into the reservoir and associated with a treatment, such as hydraulic fracturing.
Freshwater aquifers: An underground geological formation or group of formations, containing freshwater.
Horizontal drilling: Horizontal drilling starts with a vertical well that turns horizontal within the reservoir formation in order to contact more of the most productive rock. These horizontal laterals can be more than a mile long; the longer the exposure length, the more oil and natural gas is drained, and the faster it can flow. More oil and natural gas can be produced with fewer wells and less surface disturbance using horizontal drilling techniques. Horizontal drilling technology is appropriate for many, but not all, developments.
Hydraulic fracturing: Hydraulic fracturing is an essential completion technique that facilitates production of oil and natural gas otherwise trapped in low-permeability reservoir rocks. The process involves pumping fluid through the wellbore thereby exerting pressure at the target depth creating small cracks, or fractures in the rock that enable hydrocarbons to flow to the wellbore.
Hydrocarbons: Any organic compound containing only hydrogen and carbon. Hydrocarbons are one of the Earth's most important energy resources. The predominant use of hydrocarbons is as a combustible fuel source. Crude oil, natural gas and coal are principally made up of hydrocarbons.
Kickoff point (KOP): The depth in a directional well where the curve begins from the bottom of the vertical portion of a well.
Liquefied natural gas: Liquefying natural gas reduces the fuel's volume by 600 times, enabling it to be shipped economically from distant producing areas to markets. Converting natural gas to LNG (liquefied natural gas) is accomplished by refrigerating natural gas to -260° F.
Methane: The principal component of natural gas; the simplest hydrocarbon molecule containing one carbon atom and four hydrogen atoms. Methane is a greenhouse gas and has a much shorter lifetime in the atmosphere than carbon dioxide.
Natural gas: A naturally occurring mixture of hydrocarbon and nonhydrocarbon gases found in porous rock formations. Its principal component is methane.
Natural gas liquids (NGLs): A general term for liquid products separated from natural gas in a gas processing plant. NGLs include ethane, propane, butane and natural gasoline.
Permeability: Measurement of the ability of a fluid (natural gas, oil or water) to flow through a rock or other porous material.
Play: An area in which hydrocarbon accumulations or prospects of a given type occur. For example, the shale gas plays in North America include the Barnett, Eagle Ford, Fayetteville, Haynesville, Marcellus and Woodford, among many others. Outside North America, shale gas potential is being pursued in many parts of Europe, Africa, Asia and South America.
Porosity: The volume of space within rock that might contain oil and gas (like the amount of water a sponge can hold); the open or void space within rock, usually expressed as a percentage of the total rock volume. Thus porosity measures the capacity of the rock to hold natural gas, crude oil or water.
Possible reserves: The high-side estimate of resources profitable to produce with current technologies; less technical work has been done to explore and evaluate these reserves, therefore there is a high degree of uncertainty in this estimate.
Probable reserves: The midpoint estimate of resources profitable to produce with current technologies; more technical work has been done than so that there is 50 percent confidence that reserves could be above or below this figure.
Produced water: A term used to describe water produced from a wellbore along with oil and natural gas (excluding hydraulic fracturing or other treatment fluids). The characteristics of produced water vary by region. In general, small amounts of water are produced from shale formations because of the low relative permeability of the shale formation and the higher mobility of natural gas.
Proppant: Specifically sized particles mixed with fracturing fluids used in hydraulic fracturing treatments to hold narrow fractures open (usually fractions of an inch in width). In addition to naturally occurring sand grains, man-made or specially engineered proppants may also be used. Proppant materials are carefully sorted for size and shape to provide an efficient pathway for production of hydrocarbons from reservoirs to the wellbore.
Proven reserves: Reserves that can be produced with current technologies; significant exploration and development work gives a 90 percent confidence these reserves are recoverable.
Reserves: Resources profitable to produce with current technologies; due to the uncertainty in estimates of subsurface resources, companies use the terms possible, probable and proven to describe their confidence in the quantity of reserves that can be produced profitably.
Resources: That which can be recovered with current technologies but may or may not be profitable to produce (excludes methane/natural gas hydrates that may be recoverable in the future with technical advancements) estimated to exist in naturally occurring accumulations. A portion of the resources may be estimated to be recoverable, and another portion may be considered to be unrecoverable. Resources include both discovered and undiscovered accumulations.
Shale gas: Shale is a very fine-grained sedimentary rock that is easily broken into thin, parallel layers. Shale rock formations can contain a large amount of natural gas, but this gas is not necessarily mobile.
Sour gas: Natural gas that contains significant amounts of hydrogen sulfide, which must be removed for safety, to improve burning quality and to reduce emissions of sulfur dioxide when burned.
Sweet gas: Natural gas that contains little hydrogen sulfide.
Tight gas: Natural gas produced from relatively impermeable rock. Found in sedimentary layers of rock that are cemented together so tightly that it hinders extraction. Getting tight gas out usually requires enhanced technology applications like hydraulic fracturing. The term is generally used for reservoirs other than shales.
Ultimate potential: An estimate of recoverable reserves that will have been produced by the time all exploration and development activity is completed; includes production-to-date, remaining reserves, development of existing pools and new discoveries.
Unconventional natural gas resources: Unconventional natural gas deposits include coalbed methane, tight gas, shale gas and gas hydrates. These deposits are difficult to characterize but in general are often lower in resource concentration, more dispersed over large areas, and require well stimulation or some other extraction or conversion technology.
Undiscovered recoverable resources: Those resources estimated to be recoverable from accumulations believed to exist based on geological and geophysical evidence but not yet verified by drilling, testing or production.
Wet gas: Produced gas that contains natural gas liquids. Wet gas contains methane in addition to other hydrocarbons, such as ethane, propane and butane. Wet gas may also contain water and other impurities.