acid. A generic term used to describe a treatment fluid typically comprising hydrochloric acid and a blend of acid additives.
annulus. The space between a casing string and the borehole or between two casing strings.
aquifer. A water-bearing stratum of permeable rock, sand, or gravel.
biocide. An additive that eliminates bacteria in the water that produce corrosive byproducts.
blender. The equipment used to prepare the slurries and gels commonly used in fracture stimulation treatments.
borehole. A hole drilled into the earth by people in search of natural gas and oil.
breaker. An additive that reduces the viscosity of fluids by breaking long-chain molecules into shorter segments.
CAS. Chemical Abstract Service, a division of the American Chemical Society, whose objective is to find, collect, and organize publicly disclosed substance information.
CAS number. A unique number assigned by the CAS that identifies a chemical substance or molecular structure.
The List compiled from FracFocus: http://fracfocus.org/glossary of terms, and the State of California, Department of Conservation website: http://www.conservation.ca.gov/index/Pages/glossary-frk.aspx
casing. Pipe placed in an oil or gas well to (1) prevent the wall of the hole from caving in; (2) prevent movement of fluids from one geologic formation to another; (3) provide a means of maintaining control of formation fluids and pressure as the well is drilled.
casing string. Pipe that lines a well after it has been drilled. It is formed from sections of tube that have been screwed together.
collapse strength of casing. The pressure necessary to collapse a well casing, tubing, or drill pipe inside a well. The collapse strength of casing can be calculated from the yield strength of the metal and diameter of and wall thickness of the casing, tubing, or drill pipe.
conductor casing. Generally, the first string of casing in a well. It may be lowered into a hole drilled into the formations near the surface and cemented in place, or it may be driven into the ground by a special pile driver. Its purpose is to prevent the soft formations near the surface from caving in and to conduct drilling mud from the bottom of the hole to the surface when drilling starts. (Also known as “conductor pipe” and “drive pipe.”)
casing shoe. A tapered, bullet-nosed piece of equipment often found on the bottom of a casing string. The device guides the casing toward the center of the borehole and minimizes problems associated with hitting rock ledges or washouts as the casing is lowered into the well. (Also known as a “guide shoe.”)
cement. A mixture of sand, water, and a binding agent with no aggregates.
Cement Bond Log. A geophysical log that graphically displays the bond between cement and casing.
clay stabilizer. An additive that prevents clays from swelling or shifting.
conductor casing. The first casing string placed in a borehole. The purpose of the conductor is to prevent the collapse of the hole in unconsolidated material, such as soil.
corrosion inhibitor. An additive used in acid treatments to prevent corrosion of pipe by the corrosive treating fluid.
cross-linker. An additive that reacts with multiple-strand polymers to couple molecules, creating a fluid of high but closely controlled viscosity.
Darcy’s Law. The mathematical equation that quantifies the ability of fluid to flow through porous material such as rock.
data van. The truck used to monitor all aspects of the hydraulic fracturing job.
DOE. The US Department of Energy.
drilling rig. The equipment used to drill the borehole.
EPA. The US Environmental Protection Agency.
EPCRA. The Emergency Planning and Community Right to Know Act. In 1986, Congress enacted EPCRA, a statute that established requirements for federal, state, and local governments, tribes, and industry regarding emergency planning and community right-to-know” reporting on hazardous and toxic chemicals. One provision of EPCRA remains highly controversial. As the EPA notes, “All information submitted pursuant to EPCRA regulations is publicly accessible, unless protected by a trade secret claim.”
frac tank. The container used to store water or proppant that will be used for hydraulic fracturing.
friction reducer. An additive used to reduce the friction forces on tools and pipes in the borehole.
gelling agent. An additive that increases the viscosity of a fluid without substantially modifying its other properties.
groundwater. Water in a saturated zone under the earth’s surface.
GWPC. Ground Water Protection Council.
hydrology. The study of the flow of water.
intermediate casing. Provides protection against caving in of weak or abnormally pressured formations and enables the use of drilling fluids used to drill into lower formations.
intermediate casing string. The string of casing set in a well (after the surface casing but before production casing is set) to keep the hole from caving in and to seal off formations. In deep wells, one or more intermediate strings may be required.
IOGCC. Interstate Oil and Gas Compact Commission.
MSDS. Material Safety Data Sheet.
mechanical integrity. The measure of a well’s casing, tubing, packer, and cement to contain fluids traveling up and down the well without the fluids leaking into surrounding geologic formations.
natural gas. Methane CH4 (with or without impurities such as nitrogen). Natural gas is often classified as either biogenic (of biological origin) or thermogenic (of thermal or heat origin).
NGWA. National Ground Water Association.
nonfreshwater fluids. Water with total dissolved solids (TDS) of greater than 3,000 parts per million (ppm) or any other fluid used in oil and gas production, including hydraulic fracturing fluids.
other cement evaluation method. Used to determine the quality of the cement bond between a well’s casing and the geologic formations surrounding a borehole.
oxygen scavenger. An additive that prevents corrosion of pipes by oxygen.
packer. A downhole device used in completions to isolate the casing-tubing annulus from the production conduit, enabling controlled production, injection, or treatment.
perforate. To pierce holes in the casing and cement in a well to allow formation fluids, such as oil and gas, to enter into a well and to allow fluids to be injected into a geologic formation. Perforating is accomplished using a perforating gun, or perforator.
perforated interval. A section of casing that has been perforated during hydraulic fracturing.
permeability. The quantification of how easily fluids, such as oil, gas, and water, flow through the pore spaces in a geologic formation and into the borehole. Rocks have vertical, horizontal, and tangential permeability.
pH adjusting agent. An additive that adjusts the acidity/alkalinity balance of a fluid.
Poisson’s ratio. A mechanical property that can be used to predict the direction in which fractures will occur in a given geologic formation. When a geologic formation is compressed in one direction, it tends to expand in the other two directions perpendicular to the direction of compression. This phenomenon is called the Poisson effect.
production casing. The casing string set near the bottom of a completed borehole through which oil or natural gas is produced.
proppant. A granular substance (sand grains, crushed walnut shells, aluminum pellets, or other material) that is carried in suspension by the fracturing fluid. Proppant keeps fractures open in a formation when fracturing fluid is withdrawn after a fracture treatment.
radial cement evaluation log. A continuous log (graph) created by running a sonic transmitter and receiver down a well to determine the quality of the cement bond between the casing and the geologic formations surrounding a well.
reservoir. A bed of rock containing oil or natural gas.
reverse engineering. The reproduction of a product, through analysis of its structure, function, and operation.
saturated zone. The subsurface zone where the interstitial spaces of rock are filled with water.
shale. A fine-grained sedimentary rock that may contain oil or natural gas but which may not be producible naturally.
site. The location of a well including the area used for fluid storage and well treatment.
spring. The intersection of groundwater and surface water.
surface casing. The casing string set below freshwater aquifers to prevent their contamination.
surfactant. A chemical that acts as a surface active agent. This term encompasses a multitude of materials that function as emulsifiers, dispersants, oil-wetters, water-wetters, foamers, and defoamers.
total dissolved solids (TDS). The total amount of solids, such as minerals, salts, or metals, that are dissolved in a given volume of water.
toxicology. The study of symptoms, mechanisms, treatment, and detection of poisoning.
true vertical depth. The vertical distance from a point in the well (usually the current or final depth) to the surface.
tubing. A small-diameter pipe that is run inside well casing to serve as a conduit for the passage of oil and gas to the surface. Tubing can be a permanent or temporary part of the borehole.
tubing strings. The entire length of tubing in a well.
unsaturated zone. The subsurface zone where the interstitial spaces of rock contain but are not completely filled with water.
vadose zone. The subsurface zone between the surface and the unsaturated zone through which water travels.
Variable Density Log. The geophysical log that is a graphic representation of the bond between the cement and the borehole.
well. The hole made by the drilling bit, which can be open, cased, or both. Also called borehole, hole, or wellbore.
wellbore. A borehole; the hole drilled by a drill bit; also called a borehole or hole.
well stimulation. Any of several operations used to increase production by increasing the permeability of an oil- or gas-bearing formation, such as acidizing or hydraulic fracturing.
Young’s modulus. Used in drilling, it is a measure of the stiffness of elastic of a geologic formation, defined as the ratio of the stress along an axis over the strain along that axis. Young’s modulus can help determine how wide fractures are likely to be in a formation that will be hydraulically fractured.