Hydraulic Fracturing and Shale Gas Production: Technology, Impacts, and Regulations

Annulus: The space between the casing and the wellbore or surrounding rock.Biocide: An additive used in hydraulic fracturing fluids (and often drilling muds) to kill bacteria that could otherwise reduce permeability and fluid flow.Casing: Steel pipe inserted into a wellbore and cemented into place.It is used to protect freshwater aquifers or otherwise isolate a zone. Class II injection well:A well that injects fluids into a formation rather than produces fluids.A Class II injection well is a well associated with oil or natural gas production.Such wells include enhanced recovery wells, disposal wells, and hydrocarbon storage wells.Completion: Includes the steps required to drill and assemble casing, tubes, and equipment to efficiently produce oil or gas from a well.For shale gas wells, this includes hydraulic fracturing activities.Flowback water: The water that returns to the surface from the wellbore within the first few weeks after hydraulic fracturing.It is composed of fracturing fluids, sand, and water from the formation, which may contain hydrocarbons, salts, minerals, naturally occurring radioactive materials. Hydraulic fracturing (fracking or fracing):A stimulation technique performed on lowpermeability reservoirs such as shale to increase oil and/or gas flow from the formation and improve productivity.Fluids and proppant are injected at high pressure and flow rate into a reservoir to create fractures perpendicular to the wellbore according to the natural stresses of the formation and maintain those openings during production.Liquefied petroleum gas (LPG): Hydrocarbons, primarily composed of propane and butane, obtained during processing of crude oil, which are liquefied at low temperatures and moderate pressure.It is similar to NGL but originates from crude oil sources.Natural gas liquids (NGL): Hydrocarbons, typically composed of propane, butane, pentane, hexane, and heptane, obtained from natural gas production or processing which are liquefied at low temperatures and moderate pressure.They are similar to LPG but originate from natural gas sources.Perforation: A hole in the casing, often generated by means of explosive charges, which enables fluid and gas flow between the wellbore and the reservoir.1 This glossary provides definitions of technical terms used throughout this paper.The first time each term is used it is italicized.viii Play: A geologic area where hydrocarbon accumulations occur.For shale gas, examples include the Barnett and Marcellus plays.Produced water: The water that is brought to the surface during the production of oil and gas.It typically consists of water already existing in the formation, but may be mixed with fracturing fluid if hydraulic fracturing was used to stimulate the well.Proppant: Particles mixed with fracturing fluid to maintain fracture openings after hydraulic fracturing.These typically include sand grains, but they may also include engineered proppants. Reduced emission completion (REC or green completion):An alternative practice that captures and separates natural gas during well completion and workovers activities instead of allowing it to vent into the atmosphere. Seismic event:An earthquake.Induced seismicity is an earthquake caused by human activities.Wellbore: Also referred to as borehole.This includes the inside diameter of the drilled hole bounded by the rock face.Wellhead: The structure on the well at ground level that provides a means for installing and hanging casing, production tubing, flow control equipment, and other equipment for production.Workover: The repair or refracturing of an existing oil or gas well to enhance or prolong production.