Acid stimulation: Also known as acidizing, acid stimulation refers to pumping a stimulation fluid contains a reactive acid into a reservoir formation in order to improve permeability and productivity of a well (API, 2014; Schlumberger, 2017).
Annulus: The space around the pipe in a wellbore (Schlumberger, 2017).
Bow-tie: The bow-tie method is a technique commonly used in high-hazard industries for identifying operational (or process) risk. Bow-ties identify a variety of barriers and help communicate safety principles that link causal factors and subsequent actions to a specific event—such as a loss of well control event (Fraser et al., 2015).
Conventional well: A reservoir formation in which the resources can be produced commercially without altering permeability or viscosity (Houseworth, 2014).
Deepwater production: Production in water of depths greater than 125 meters (EIA, 2016).
Frac pack: An approach that combines the production improvement from hydraulic fracturing with the sand control provided by gravel packing. It involves simultaneous hydraulic fracturing of a reservoir and the placement of a gravel pack with the objective of achieving a high-conductivity gravel pack to create a conduit for the flow of reservoir fluids at lower pressures (Sanchez and Tibbles, 2007).
Fracture gradient: The pressure necessary to initiate and propagate fractures in a rock at a particular depth in a well (Schlumberger, 2017).
Gravel pack: A sand-control method used to prevent production of formation sand in which a steel screen is placed in the wellbore and the surrounding annulus is packed with prepared gravel of a specific size (Schlumberger, 2017).
Hydraulic fracturing: A controlled, high-pressure injection of fluid and proppant into a well to generate fractures in the rock formation containing the oil or gas, used to increase production of oil and gas (NASEM, 2017).
Hydrocarbon: Any organic compound, gaseous, liquid, or solid, consisting solely of carbon and hydrogen (USGS, 2014).
Proppant: Sand or ceramics that help keep hydraulic fractures open after fluid injection is completed. The injected fluid can comprise water and small amounts of chemical additives that reduce friction in the pipe and help carry the proppant into the fractures (NASEM, 2017).
Reservoir: A subsurface, porous, permeable body of rock in which oil or gas resources have accumulated (USGS, 2014).
Sandstone: Sedimentary rock composed of abundant rounded or angular fragments of sand set in a fine-grained matrix (silt or clay) (USGS, 2002).
Treatment fluid: A fluid used to resolve a specific wellbore or reservoir condition, such as stimulation, isolation, or control of reservoir gas or water (Schlumberger, 2017).
Unconventional well: A well in which oil and/or gas is extracted using stimulation or techniques including hydraulic fracturing. Fracturing is needed to extract economic quantities of oil and gas (NASEM, 2017).
Well control: Method for maintaining pressure on open formations to prevent or direct the flow of formation fluids into the wellbore, including procedures to safely stop a well from flowing should an influx of formation fluid occur (Schlumberger, 2017).
Well stimulation: A type of treatment where the rate of oil flow from the reservoir to the well is increased in situations where the natural reservoir flow characteristics are not favorable and require improvement for effective oil recovery (Houseworth, 2014).
Wellbore: A drilled hole to aid exploration and recovery of natural resources including oil, gas or water. Wellbore can be cased using materials such as steel casing and cement, or it may be uncased (Petropedia, 2018).