Glossary of Terms

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abandoned well — A well no longer in use.


access roads — Roads that allow for traffic to move to and from the well pad.


allostatic load — The “wear and tear” on the body due to exposure to repeated or chronic stress.


aquifer — A permeable rock layer through which water flows.




blowout — A sudden rush of oil or gas from beneath the ground to the surface through the wellhead.


boom-and-bust cycle — A sharp increase in a community’s economic growth due to an economic stimulus, such as natural resource development, accompanied by a significant, temporary population influx, followed by a sharp economic decline when the project closes and the population falls.


boomtown — A community that undergoes the boom-and-bust cycle.


brackish water — Water whose salt content falls between that of fresh and salt water.




casing — Steel and cement lining the wellbore intended to seal off the well from the surrounding rock.


CO — The chemical formula for carbon monoxide, a colorless, odorless gas that forms from the partial oxidation of carbon-containing compounds. It is toxic to humans at concentrations above approximately 35 parts per million and plays a role in the formation of ground-level ozone.

compressors — Machines that pressurize gas and vapor to create a pressure gradient and force natural gas to move in a desired direction through pipelines.


containment pond — A pond, which can be lined or unlined, used for the disposal or treatment of wastewater.


crowding out — A phenomenon that occurs when increasing economic activity and population influx lead to higher local prices, causing some local businesses on the margin to fail, which can decrease the economic diversity in a community.




decibels (dB) — A measurement of sound. Db(A), or decibels adjusted for human hearing frequencies, is a standard measurement of environmental noise.


deforestation — The process of cutting down trees to clear land in a forested area.


distribution lines — or “mains,” are a type of natural gas pipelines that carry gas under reduced pressure from large high-pressure transmission lines to low-pressure customer service lines.


drill cuttings — Rock fragments generated by the drill bit.


drilling mud — Fluids used to lubricate and maintain pressure in the well during drilling (also: drilling fluid).


drilling unit — An area designated by the state that can contain an oil or gas well. The allotted acreage can vary widely by state.




easement — Financial compensation to a private property owner for the use of their land for public purposes, such as the passage of an interstate natural gas transmission line.


eminent domain — A legal process by which a state, municipality, private person, or corporation can acquire rights to private property for public use. Allowed under the Fifth Amendment of the Constitution of the United States and referenced in most state constitutions, eminent domain is specifically granted for interstate natural gas transmission pipelines under the 1938 Natural Gas Act.


erosion — The process of water removing particles of soil and rock as it flows from high to low ground and depositing it elsewhere.


evaporation pits or ponds — Surface areas of standing wastewater. Water, along with some chemicals contained in the wastewater, is allowed to evaporate into the air, leaving behind a concentrated solution of chemicals for disposal.


exploratory well — A well drilled to determine the productivity of a well site and determine future productivity potential of the site.




federal regulatory water rights — Regulatory constraints (such as Endangered Species Act requirements) that often trump other water laws.


federal reserved right doctrine — The doctrine stipulating that American Indian tribes retain rights to water, even if those rights were not specifically allocated to them in treaties with the U.S. government.


fissures — Small cracks in a rock formation.


flaring — The process of burning off excess natural gas.


flowback fluid — The fluid that initially returns to the surface after being injected in the shale formation to fracture the rock; it contains both the original fracturing fluid and some constituents from the formation, which can include salts, heavy metals, volatile organic compounds, and naturally occurring radioactive materials (NORM).


flowlines — a network of low-pressure pipes that connect oil or gas wells to a gathering station.


fluid retention pond — Basins intended to hold fluids that have already been used in the drilling process. They are lined with oil resistant materials to prevent leaching. 


forced pooling — The state’s ability to incorporate adjacent plots of land into a drilling unit.


formation water — Naturally occurring water found in geological formations below the surface of the earth.


fugitive emissions — Gases that unintentionally leak out of oil and gas equipment and infrastructure.




gathering lines — A type of natural gas pipeline that carries the gas from a production facility to a compressor station or processing plant.


geophysical prospecting — Quantitative testing to determine the character of the underlying rock formations.


green completion — A process that separates commercially useful hydrocarbons from the flowback water issuing from the well during the well completion stage; it captures many of the volatile organic compounds emitted during this stage.


green fracturing fluids — Fluids that differ from traditional fracturing solutions by removing some of the more harmful chemicals and reducing the solution volume.


greenhouse gases — Gases that contribute to the greenhouse gas effect: gases in the atmosphere that trap and reflect heat back to the earth, significantly affecting its temperature. 




health-related quality of life (HRQOL) — A person’s or group’s perception of physical and mental health over time.


hydraulic fracturing — The process of injecting a liquid formulation of chemicals and water into a geologic formation at high pressure to fracture the formation and extract trapped hydrocarbons (i.e., oil and gas).




impoundment — A body of water that is completely enclosed.


infilling — The process of drilling multiple wells at an extraction site that a company determined to be worth investment and development.


in-migration — A significant population movement into a particular geographic area, often drawn by real or perceived economic opportunities.




landmen — Representatives of an oil company or independent speculators who negotiate oil and gas leases.


lease (oil and gas) — a legal agreement between a mineral owner and another party that grants the exclusive rights to drill or produce oil or gas in an area of land defined by the lease.


leaching — The slow leaking of liquids out of a holding area or container.


local gathering station — A junction point that connects gathering lines from

the well heads in an area, collecting gas or oil into a central location.




mineral owner — The owner of a property’s subsurface minerals; the mineral owner is not necessarily the same as the owner of the surface land above the minerals. 


methane — The main component of natural gas with the chemical formula CH4, methane is a flammable gas that can act as a greenhouse gas.




noise impact assessment — An evaluation that sets baseline amounts for ambient noise and identifies populations at risk for elevated noise.


noise mitigation plan — A plan to avoid problems that arise when too much noise is present in an area.


NOx — refers to the mono-nitrogen oxides nitric oxide (NO) and nitrogen dioxide (NO2), formed when nitrogen and oxygen gases in the air react during combustion, including of natural gas. In the presence of sunlight, NOx can interact with volatile organic compounds to produce ground-level ozone.




orphaned well — Old, historically abandoned wells that have not been properly decommissioned and plugged.


open pit — Usually designed to hold wastewater, any uncovered containment hole in the ground.


operator — A person or company that operates the well and oversees the drilling operation at every stage.




particulate matter (PM) — A complex mixture of small airborne particles and liquid droplets. Depending on their size (EPA is concerned with those 10 micrometers in diameter or smaller), they can cause serious health effects if inhaled.


plat — A map drawn to scale that shows the division of land. Such maps become legally valid when approved by a local government authority.


plugged well — A well determined to be unproductive and capped by the company.


prior appropriation doctrine — the water law regime that predominates in the Western United States, under which water is allocated in specific amounts for “beneficial use.” Each water right has a priority date that determines its place in the hierarchy of withdrawals, and it maintains the same date even if it is sold to another user.


processing plant — Site where crude gas or oil is transported to be converted into a refined, workable form. It can be located on or off the well pad site. 


produced water — wastewater that emerges from the well along with the oil or gas; it is mostly composed of water from the target formation (see: formation water), which can contain salts, heavy metals, volatile organic compounds, and naturally occurring radioactive materials.


proppant — Sand grains or similar materials added to the fracturing fluids and used to hold fissures open to allow oil or gas to flow out of the rock formation.




reclamation law — Specialized area of federal contract law for federal reclamation projects, such as California’s Central Valley Project.


re-stimulation — Hydraulically fracturing a previously fractured well to release more gas or oil.


riparian doctrine — The water law regime that predominates in the Eastern United States, under which landowners along waterways have a rights to the natural quantity and quality of flow in the waterway, except as diminished by the “reasonable use” of the water by other riparian landowners.


royalty — An interest in gas and oil production. The royalty owner receives a percentage of the production from the lease area. 




sedimentation — Particles suspended in fluid flow, which can be a source of pollution of waterways. 


seismic survey — Monitored seismic test waves that reveal underground rock formations.


setback — Where applicable, the required distance that the development operation must legally maintain from residences or other sensitive areas.


severance taxes — Taxes levied on the extraction of natural resources from the earth.


shale development — the process of seeking and extracting oil and/or natural gas reserves from shale deposits using a combination of horizontal drilling and high-volume hydraulic fracturing techniques to reach and break open previously inaccessible “tight” geologic formations like shale deposits, allowing the trapped resources to flow into the well and up to the surface for capture.


shale play — An area where shale formations potentially containing natural gas and oil are present.


shale formation (shale rock) — Fine-grained sedimentary rock formations of mostly compacted clay and mud.


siting — The process of choosing the appropriate place to locate a drilling operation.


SO2 — The chemical formula for sulfur dioxide, a toxic air pollutant that can lead to acid rain.


sour gas — Gas containing significant amounts of hydrogen sulfide (H2S), a highly toxic gas with an odor of rotten eggs.


split estate — A property whose subsurface minerals do not belong to the surface owner, but have been previously separated, sold, or allotted to another owner.


staking (a well site) — Mapping out the area where the company intends to locate a well pad and marking it with stakes. States sometimes require operators to do this in order to obtain a drilling permit.


sweetening — The process of removing sulfur from the natural gas produced from a well.




thumper truck — Used in seismic exploration, a truck carrying a heavy weight that is dropped on to hard surfaces to generate a seismic pulse.


total dissolved solids (TDS) — Dissolved organic and inorganic substances contained in a liquid; salts are a key component. TDS levels are used as an indication of water quality.


transmission lines — a type of natural gas pipeline that carries the gas over long distances, transporting processed gas to and from storage facilities and compressor stations, and then to distribution lines.




venting — The process of releasing excess gas into the atmosphere.


viewshed — The landscape or scenery visible to the eye from a fixed vantage point.





wastewater — Water that has previously been used in the hydraulic fracturing process and contains fracturing-related compounds.


well pad — The central site containing one well or multiple wells and associated equipment and infrastructure.


well spacing — The permissible proximity of wells within one geological formation, as determined by the state.


wellbore — A bore or hole created by the drill bit.  


wellhead (also known as a “Christmas tree”) — A set of pressure gauges and control valves that control the flow of gas or oil and maintain set conditions at the surface of the well. 


workover — An extensive overhaul of the equipment on the well pad during the production phase.