Class II Injection Wells
Class II wells are used only to inject fluids associated with oil and natural gas production. 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. Approximately 180,000 Class II wells are in operation in the United States.
Class II wells fall into one of three categories.
Enhanced recovery wells
Hydrocarbon storage 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. 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.
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.
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.
Under Section 1422 states must meet EPA’s minimum requirements for UIC programs.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 (see Details in UIC Page