Class II Injection Wells: Injection Wells Related to Oil and Gas Activity
Class II injection wells have been used in oil field related activities since the 1930’s. Today there are approximately 170,000 Class II injection wells located in 31 states. All Class II injection wells are regulated by either a state agency which has been granted regulatory authority over the program, or by USEPA. Class II wells are subject to a regulatory process which requires a technical review to assure adequate protection of drinking water and an administrative review defining operational guidelines. The evaluation of the site suitability for a Class II injection well is very similar to that for a Class I nonhazardous waste inject ion well. The site’s subsurface conditions are evaluated to make sure the formations will keep the fluids out of drinking water sources. The wells must be constructed to protect USDWs, and wells are tested and monitored periodically to ensure no drinking water is being negatively impacted by the operations.
Class II wells are categorized into three subclasses: salt water disposal wells, enhanced oil recovery (EOR) wells, and hydrocarbon storage wells.
Salt Water Disposal Wells
As oil and natural gas are brought to the surface, they generally are mixed with salt water. On a national average, approximately 10 barrels of salt water are produced with every barrel of crude oil. Geologic formations are selected to receive the produced waters, which are reinjected through disposal wells and enhanced recovery wells. These wells have been used as a standard practice in the oil and gas industry for many decades and are subject to authorization by regulatory agencies.
Enhanced Oil Recovery Wells
Enhanced Oil Recovery (EOR) injection wells are used to increase production and prolong the life of oil-producing fields. Secondary recovery is an EOR process commonly referred to as water–flooding. In this process, salt water that was co–produced with oil and gas is reinjected into the oil-producing formation to drive oil into pumping wells, resulting in the recovery of additional oil. Tertiary recovery is an EOR process that is used after secondary recovery methods become inefficient or uneconomical. Tertiary recovery methods include the injection of gas, water with special additives, and steam to maintain and extend oil production. These methods allow the maximum amount of the oil to be retrieved out of the subsurface. Approximately 60% of the salt water produced with oil and gas onshore in the United States is injected into EOR wells.
Hydrocarbon Storage Wells
Hydrocarbon storage wells are generally used for the underground storage of crude oil and liquid hydrocarbons* in naturally occurring salt or rock formations. The wells are designed for both injection and removal of the stored hydrocarbons. The hydrocarbons are injected into the formation for storage and later pumped back out for processing and use.
From the Ground Water Report to the Nation