Water: Class II
Class II Wells - Oil and Gas Related Injection Wells (Class II)
Class II Well Questions
This page describes the various types of Class II wells and their uses.
It also explains how the use of Class II wells protects drinking water resources, and presents the UIC Program requirements for Class II wells to ensure the protection of underground sources of drinking water (USDWs).
Class II Wells
What is a Class II well?
Class II wells inject fluids associated with oil and natural gas production. Most of the injected fluid is salt water (brine), which is brought to the surface in the process of producing (extracting) oil and gas. In addition, brine and other fluids are injected to enhance (improve) oil and gas production. The approximately 144,000 Class II wells in operation in the United States inject over 2 billion gallons of brine every day. Most oil and gas injection wells are in Texas, California, Oklahoma, and Kansas.
What are the types of Class II wells?
Three types of Class II injection wells are associated with oil and natural gas production.
- Enhanced Recovery Wells inject brine, water, steam, polymers, or carbon dioxide into oil-bearing formations to recover residual oil and—in some limited applications—natural gas. This is also known as secondary or tertiary recovery. The injected fluid thins (decreases the viscosity) or displaces small amounts of extractable oil and gas, which is then available for recovery. In a typical configuration, a single injection well is surrounded by multiple production wells. Production wells bring oil and gas to the surface; the UIC Program does not regulate wells that are soley used for production. However, EPA does have authority to regulate hydraulic fracturing when diesel fuels are used in fluids or propping agents. During hydraulic fracturing, another enhanced recovery process, a viscous fluid is injected under high pressure until the desired fracturing is achieved, followed by a proppant such as sand. The pressure is then released and the proppant holding the fractures open allows fluid to return to the well. Enhanced recovery wells are the most numerous type of Class II wells, representing as much as 80 percent of the approximately 151,000 Class II wells.
- Disposal Wells inject brines and other fluids associated with the production of oil and natural gas or natural gas storage operations. When oil and gas are produced, brine is also brought to the surface. The brine is segregated from the oil and is then injected into the same underground formation or a similar formation. Class II disposal wells can only be used to dispose of fluids associated with oil and gas production. Disposal wells represent about 20 percent of Class II wells.
- Hydrocarbon Storage Wells inject liquid hydrocarbons in underground formations (such as salt caverns) where they are stored, generally, as part of the U.S. Strategic Petroleum Reserve. There are over 100 liquid hydrocarbon storage wells in operation.
How do Class II wells protect drinking water resources?
When oil and gas are extracted, large amounts of brine are typically brought to the surface. Often saltier than seawater, this brine can also contain toxic metals and radioactive substances. It can be very damaging to the environment and public health if it is discharged to surface water or the land surface. By injecting the brine deep underground, Class II wells prevent surface contamination of soil and water.
When states began to implement rules preventing disposal of brine to surface water bodies and soils, injection became the preferred way to dispose of this waste fluid. All oil and gas producing states require the injection of brine into the originating formation or into formations that are similar to those from which it was extracted.
What are the requirements for Class II wells?
A state has the option of requesting primacy for Class II wells under either section 1422 or 1425 of the Safe Drinking Water Act:
Section 1422 requires states to meet EPA’s minimum requirements for UIC programs. Programs authorized under section 1422 must include construction, operating, monitoring and testing, reporting, and closure requirements for well owners or operators. Enhanced oil and gas recovery wells may either be issued permits or be authorized by rule. Disposal wells are issued permits. The owners or operators of the wells must meet all applicable requirements, including strict construction and conversion standards and regular testing and inspection.
Section 1425 allows states to demonstrate that their existing standards are effective in preventing endangerment of USDWs. These programs must include permitting, inspection, monitoring, and record-keeping and reporting that demonstrates the effectiveness of their requirements.
Visit the Regulations page to read more about the requirements for owners and operators of Class II wells.
- The Reporting Forms page provides links to the forms used by Class II well operators and primacy programs to report and demonstrate that injection operations are protecting USDWs.
- Read about Hydraulic Fracturing Under the Safe Drinking Water Act.
- The Guidance page presents links to guidance documents prepared by the UIC Program.