Additive Any substance or combination of substances or constituents that is combined with a base fluid (typically water) and proppant (typically sand) to create a "fracturing fluid," which is then pumped into the formation. Examples of common additives include: crosslinkers, biocides, buffers, fluid-loss additives, stabilizers and breakers.
Aquifer A water-bearing formation that usually resides near the ground surface and generally contains fresh water. Aquifers are typically separated from the deep rock formations that undergo fracture stimulation by thousands of feet (and millions of tons) of solid, impermeable rock.

Base Fluid A liquid or foam substance into which additives are mixed or added to comprise a fracturing fluid system. The base fluid for many hydraulic fracturing systems is water. In certain other applications, it may also be a carbon dioxide- or nitrogen-based foam.

Cased hole A section of the wellbore in which casing and cement is installed.
Casing Steel pipe that's used to line the inside of the wellbore -- both for the purpose of stabilizing its structure, and, when cemented, to help prevent the movement of fluid between formations.
Cementing The process of placing cement slurry around the outside of the casing to stabilize the wellbore and prevent fluid movement between formations.
Chemical Family A group of elements in the Periodic Table, or more commonly, compounds that share certain physical and chemical characteristics and a common name. Examples include: the alkaline earth metals, rare gases, carboxylic acids and ketones.
Constituent A discrete chemical component used to form the additives involved in the fracturing process. Constituents often are identified through the Chemical Abstracts Service (CAS) system, which is a unique numerical indicator assigned to most chemicals.

Drainage Radius The radius of the approximate circular shape around a single wellbore from which the hydrocarbon flows into the wellbore. The drainage radius of a single well will help determine how many wells will be needed (and where they should go) to most efficiently drain the reservoir.

Flowback Water The water that returns to the surface via the wellbore after the fracturing treatment is complete.
"Fracking", "Fracing" or Fracture Stimulation All variations of the term "hydraulic fracturing," and generally used synonymously with it.
Fracturing Fluid A fluid mixture typically consisting of one or more additives, a base fluid (typically water) and a proppant (typically sand) that's pumped into a well under pressure to induce fractures in the target geologic formation. The fractures expose more of the formation to the operator, and provide a conduit for hydrocarbons to flow to the wellbore. This results in improved production of oil or natural gas. The specific elements used in a given fracturing operation will vary depending on a number of factors, including depth, temperature and myriad geological considerations.