Class II wells are used to inject fluids associated with oil and natural gas production. This well class may be referred to as the Underground Injection Control program or "UIC" wells.
Class II fluids are primarily brines (salt water) that are brought to the surface while producing oil and gas.
Class II wells in North Dakota may be used for saltwater disposal or injection for enhanced oil recovery.
Frequently Asked Questions
The Underground Injection Control program (UIC) is a nationwide program pursuant to the Safe Drinking Water Act (SDWA) and is overseen by the Environmental Protection Agency (EPA). The UIC program was established to protect underground sources of drinking water (USDW) by regulating the permitting, construction, operation and closure of injection wells that place fluids underground. There are six classes of UIC wells and the Department of Mineral Resources has primacy over Class II and Class III wells.
The cornerstone of the UIC Program is three layers of protection for USDW's. An injection well's construction with three layers of protection helps to ensure that groundwater is protected. The first layer of protection is surface casing-a steel pipe that is encased in cement that reaches from the ground surface to below the deepest USDW. The second layer of protection is the production casing-a pipe placed in the wellbore from the ground surface to the well's total depth and permanently cemented in place above the injection formation. The third layer of protection is the injection tubing string and packer that conducts the injected fluid down to the perforations at the bottom of the well for injection into an underground formation. With these well construction standards, all three layers of protection would have to fail at the same time for injection to potentially impact groundwater.
Primacy allows states to implement programs through agreements with the EPA unique to their own geology in order to protect USDW's. North Dakota's UIC regulations meet or exceed federal regulations. EPA approval of a primacy program allows state programs to differ from federal rules and guidance, as well as from other states, as long as the program is as effective as federal regulations in protecting USDW's.
Class II injection wells are regulated by the Oil and Gas Division, while Class III wells are regulated by the Geological Survey. In North Dakota, Class II injection wells are used for enhanced oil recovery and oilfield waste disposal, which is typically saltwater (brine). Class III wells are used for injecting fluids associated with subsurface mineral mining. While there are no Class III wells currently in operation in the state, there are a growing number of active Class II wells.
Enhanced oil recovery wells are used to help extract additional oil and natural gas resources that primary recovery was unable to produce. Injection of fluids or gases into the reservoir moves or "pushes" the oil or natural gas to surrounding producing wells, making the resource available for production. Without enhanced recovery methods these additional oil and gas resources would not be recovered.
Saltwater is a waste product that is produced and separated from oil during the production process. In North Dakota, just over one barrel of saltwater is produced for every one barrel of oil. Generally, this saltwater is too salty to be recycled so it must be injected underground well below USDW's. SWD's are the only approved method for disposing of saltwater in North Dakota.
Each injection well requires public notice and hearing before a permit may be issued unless it is within an area permit, (which previously had a public hearing) which allows administrative approval. Area permits are specified by field and were originally allowed when North Dakota received primacy in 1983. This essentially grandfathered some areas of the state into the program.
Construction of these wells is carefully planned and monitored to protect groundwater sources, with the typical well having three layers of steel casing/tubing as well as two layers of cement. Once a well begins injection, pressure and wellbore integrity are carefully monitored once a month by our inspectors and a down-hole mechanical integrity test is required initially and at least every five years or whenever the down-hole portion of the well has undergone maintenance.
Other requirements for the permitting process:
- Surface owners within 1/4 mile must be notified.
- SWD's over shallow aquifers require a geotechnical analysis by a qualified, independent contractor before a proposed location will be considered. This is to determine the suitability of the shallow subsurface geology to protect the shallow aquifer.
- Injection must be into a formation with an upper and lower confining zone to prevent migration of fluids into other formations or fresh water zones. In North Dakota, the disposal zone is typically one half mile to one mile below the surface, into the Dakota Group.
Mechanical integrity tests are meant to test the ability of the wellbore, consisting of casing, tubing and packer to contain injection pressure and injected fluids. The tubing and packer are the primary containment system that is monitored and inspected monthly by Oil and Gas Division field inspectors. The casing and cement are the backup containment system. Mechanical integrity tests are meant to insure that the primary containment system does not leak and ensures the back-up system will hold if the primary system (tubing and packer) fail between monthly inspections
At the beginning of each month, operators of injection wells must submit to the Oil and Gas Division the beginning and end of month meter readings, the total volume of fluid injected, average injection pressure, a list of the individual sources of fluid, the type of fluid that was injected and the transportation method (piped or trucked) of the fluid.
North Dakota geology is very suitable for underground injection of oil and gas wastes. Disposal injection in North Dakota is typically one-half mile below the deepest underground source of drinking water (USDW) and one mile to two miles above the granite rock formations where earthquakes originate. However, as a precaution North Dakota has rules in place relative to induced seismicity: North Dakota requires a map depicting the area around the location where the disposal well is proposed that depicts any known or suspected faults. Wells must be constructed in a manner that prevents movement of fluids into USDW's or into unauthorized zones. The North Dakota Industrial Commission (NDIC) may require continuous monitoring up to and including seismic monitors as well as sampling injected fluids and testing of the well. The NDIC can modify or suspend the well permit at any time. In addition the NDIC may order the operator to cease injection of a well should it become noncompliant.
Current science indicates that earthquakes originate from faults in the granite rock formations that are much deeper and older than the sedimentary rocks where disposal injection occurs in North Dakota. Other states may have induced seismic activity due to some instances of fluid injection into very deep formations just above the granite rock formations. The Interstate Oil and Gas Compact Commission (IOGCC) recently concluded a review of the potential for injection induced seismicity associated with Oil and Gas Development. North Dakota did not provide data for the primer, but state regulators participated as technical advisors to the IOGCC working group. Access to this study benefits North Dakota citizens and regulators alike. We encourage North Dakotans to review the IOGCC document and become informed on our states very low risk for seismic activity. Specific examples of how low risk North Dakota geology is, as well as how North Dakota compares to states with known stresses or faults can be found on pages 9 and 107 of the IOGCC study. For state regulators, this document provides valuable insight from other states with known induced seismicity. If a very unlikely event should occur in our state, North Dakota regulators can draw on the experience of others to make informed decisions.
In early 2016 the United States Geological Survey released a one year induced seismicity risk assessment, which detailed six states that are at risk for earthquakes due to deep water injection. North Dakota is one of the forty-four states determined to not be at risk for induced seismicity.
Treating plants are closely related to the Oil and Gas Division's UIC program and have similar requirements, because both treating plants and SWD's handle oilfield waste and sometimes share the same location. Treating plants separate oilfield wastes such as drill cuttings and tank bottoms from the oil and saltwater. Recovered oil is then sold, while the cuttings and other separated waste are dried for burial in special waste landfills. Saltwater is disposed of in the onsite SWD or at another authorized SWD. If the location is not shared, saltwater is trucked or piped to the offsite SWD. Treating plants are similar to a recycling facility in that they recover additional resources and prolong the life of special waste landfills.
When any well is plugged in North Dakota, it must first receive approval of the plugging procedure and the plugging operations are then witnessed by an Oil and Gas Division field inspector. Typically, cement is pumped down hole to isolate, or "seal-off" the injection zone from the well bore and other formations. A tool, called a cement retainer, is placed down hole to "squeeze" or pump cement into any perforations that had been placed into the casing. Otherwise, cement is placed like a "plug" in the wellbore. Additional cement plugs are set in the well bore to permanently isolate oil, gas, and water formations from fresh water formations and to seal the well bore at the surface. The well casing is cut off deep enough to prevent interference with agriculture or utility construction and a metal plate is welded onto the cut-off casing.