Shale Oil and Gas Drilling – Glossary of Terms
An assembly of valves installed on the wellhead that are designed to control any sustained heavy flow of oil or gas that may be encountered while drilling the well.
Saline geological formation water resulting from, obtained from, or produced in connection with exploration, drilling, well stimulation, production of oil or gas, or plugging of a well.
A fluid used in drilling a borehole in the earth. Drilling mud serves several purposes:
- helps control formation pressure during drilling
- keeps fluids from the rock formation from entering the borehole
- cools and lubricates the drill bit
- stabilizes the well bore and prevents damage to the target formation
- circulates cuttings out of the borehole
Different fluids can be used as drilling mud, depending on factors such as the well type and rock formation that will be drilled. Some drilling muds are water-based while others are oil-based. It is less common today to use oil-based mud. Synthetic-based muds are more commonly used in place of oil-based muds of the past because synthetic muds perform well, have less environmental impact and have faster biodegradability.
Rock and soil fragments that are excavated from a borehole while drilling oil or gas wells. At the surface, drill cuttings are separated from the drilling mud through shale shakers.
After the hydraulic fracturing procedure is complete, internal pressure in the geologic formation forces a percentage of fluid (estimated at 10-20 percent of the total volume injected) back to the surface through casing in the wellbore. The returned fluid is commonly referred to in the industry as “flowback” fluid.
Gas processing plant
A facility that recovers liquid hydrocarbons such as ethane from wet natural gas.
A buried system of pipelines used to transport oil and/or gas from the wellhead to a main pipeline.
A drilling method where a well is drilled thousands of feet downward and then gradually angled out horizontally (up to 90 degrees) through the targeted shale formation. With horizontal drilling, a much greater portion of the target formation is exposed for production as opposed to a vertical well bore.
After the well is drilled and production casing has been installed and cemented, a mixture of water, sand and chemical additives is injected under pressure to fracture the shale, which enhances the flow of oil and/or gas to the wellbore. Hydraulic fracturing is a stimulation technique that has been used in the oil and gas industry since the 1950s. Water used to fracture a well usually comes from a stream, river, reservoir or lake near the drill site, or in some cases, from a local municipal water plant.
Natural gas (or “dry” natural gas)
An efficient, clean-burning gas. Natural gas is widely used in homes and businesses. Before it is refined, natural gas is actually a mixture of gases. After refining, natural gas delivered to the home is almost pure methane.
Natural gas liquids (NGLs)
Heavier hydrocarbons found in natural gas including ethane, propane , butane and natural gasoline that may be extracted or isolated as liquefied petroleum. NGLs removed from the gas stream are valuable as raw materials to produce chemicals, plastics and gasoline.
Natural gas processing
Before becoming suitable for pipeline transmission and use, extracted natural gas may be processed to remove water and impurities such as hydrogen sulfide, nitrogen and carbon dioxide. Wet natural gas is processed to recover heavier hydrocarbons (called natural gas liquids).
Production tree (or “Christmas tree”)
The assembly of above-ground valves, pipes and fittings used to control the flow of oil and gas from the casing head at an oil or gas well. It is sometimes called a Christmas tree because it generally resembles a decorated tree.
In the hydraulic fracturing process, sand is added to the hydraulic fracturing fluid. Once the hydraulic fracturing process ends, sand remains in the fractures in the shale and serves to “prop” open the induced fractures, thereby increasing the permeability as well as the productive capability of the shale.
Steel pipe installed and cemented in an oil or gas well as drilling progresses. Casing does the following:
- prevents contamination of aquifers;
- prevents escape of oil or natural gas to the environment;
- stabilizes the well bore;
- seals the well bore to prevent blow-outs;
- prevents fluid loss during drilling; and
- isolates undesirable hydrocarbon or fluid bearing flow zones.
The steps taken after a well is drilled to put it into production. These include:
- installation and cementing of production casing;
- perforating the production intervals;
- hydraulic fracturing of those intervals;
- installing production equipment; and
- connecting the flow line from the well to the sales pipeline.
A general term for the components/equipment at the surface of an oil or gas well (See also Production Tree).
Wet natural gas
Natural gas containing liquid hydrocarbons in solution.
Disclaimer: This glossary has been created by the Ohio Environmental Protection Agency (Ohio EPA) and Ohio Department of Natural Resources (ODNR) as a general resource to help citizens understand some of the common terminology used in the oil and gas industry, specifically related to drilling operations.
This glossary is intended as a general resource only to provide “plain English” descriptions of common terms. The descriptions contained in this glossary do not supersede or replace any definitions for terms that may be currently included in either the Ohio Revised Code or Ohio Administrative Code.