Saltwater Disposal Well

Saltwater Disposal Well


Underground Injection Control (UIC).

Class II Oil and Gas Related Injection Wells.

Use of Class II wells

Class II wells are used only to inject fluids associated with oil and natural gas production. Class II fluids are primarily brines (salt water) that are brought to the surface while producing oil and gas.  It is estimated that over 2 billion gallons of fluids are injected in the United States every day. Most oil and gas injection wells are in Texas, California, Oklahoma, and Kansas.

The number of Class II wells varies from year to year based on fluctuations in oil and gas demand and production. Approximately 180,000 Class II wells are in operation in the United States.

Class II wells fall into one of three categories.

  • Disposal wells
  • Enhanced recovery wells
  • Hydrocarbon storage wells

Class II well types

Disposal wells

During oil and gas extraction, brines are also brought to the surface. Brines are separated from hydrocarbons at the surface and reinjected into the same or similar underground formations for disposal. Wastewater from hydraulic fracturing activities can also be injected into Class II wells.

Class II disposal wells make up about 20 percent of the total number of Class II wells.

Enhanced recovery wells

Fluids consisting of brine, freshwater, steam, polymers, or carbon dioxide are injected into oil-bearing formations to recover residual oil and in limited applications, natural gas.

The injected fluids thin (decrease the viscosity) or displace small amounts of extractable oil and gas. Oil and gas is then available for recovery. In a typical configuration, a single injection well is surrounded by multiple production wells that bring oil and gas to the surface.

The UIC program does not regulate wells that are solely 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 holds the fractures open to allow fluid to return to the well.

Enhanced recovery wells are the most numerous type of Class II wells. They represent as much as 80 percent of the total number of Class II wells.

Hydrocarbon storage wells 

Liquid hydrocarbons are injected into underground formations (such as salt caverns) where they are stored, generally, as part of the U.S. Strategic Petroleum Reserve.

Over 100 liquid hydrocarbon storage wells operate in the United States.

Protecting drinking water resources 

Extraction of oil and gas usually produces large amounts of brine. Often saltier than seawater, this brine can contain toxic metals and radioactive substances. Brines can damage the environment and public health if discharged to water or land. Deep underground injection of brines in formations isolated from underground sources of drinking water prevents soil and water contamination.

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 similar formations.

Class II well requirements

States (including federally recognized tribes and U.S. territories) have the option of requesting primacy for Class II wells under either Section 1422 or 1425 of the SDWA.

Under Section 1422 states must meet EPA’s minimum requirements for UIC programs. Programs authorized under section 1422 must include well owner and operator requirements for:

  • Construction
  • Operation
  • Monitoring and testing
  • Reporting
  • Closure requirements

Under Section 1422 enhanced 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.

Under Section 1425 states must demonstrate that their existing standards are effective in preventing endangerment of USDWs. These programs must include requirements for:

  • Permitting
  • Inspections
  • Monitoring
  • Record-keeping
  • Reporting

Information source: United States Environmental Protection Agency

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