A wide variety of outcomes are possible when contemplating the likelihood that an oil or natural gas injection well could increase the chance of seismic activity, including the possibility of not operating the well at all, according to a draft report by a U.S. Environmental Protection Agency's (EPA) workgroup.
The EPA researchers found that three components are necessary for significant injection-induced seismicity: stressed faults, pressure buildup from disposal activities and a pathway for increased pressure to communicate with the fault. They noted that "no single recommendation addresses all of the complexities related to injection-induced seismicity, which is dependent on a combination of site geology, geophysical and reservoir characteristics.
"An absence of historical seismic events in the vicinity of a disposal well does not provide assurance that induced seismicity will not occur; however, this absence may be a supportive indicator of induced seismicity if it occurs following activation of an injection well. Proof of induced seismicity is difficult to achieve, but it is not a prerequisite for prudent action."
The researchers developed a decision model to inform EPA's Underground Injection Control management about site assessment strategies and practical approaches for assessing the three components necessary for injection-induced seismicity. If issues are identified through site assessment and no approach can be used to address those issues, "do not operate [the] well," according to the decision model.
The 341-page document, "Minimizing and Managing Potential Impacts of Induced-Seismicity from Class II Disposal Wells: Practical Approaches," was authored by EPA's Underground Injection Control National Technical Workgroup. The draft, which was completed late last year, was recently released by EPA in response to a Freedom of Information Act request by EnergyWire.
"The draft technical report uses the existing regulatory framework for Class II underground injection wells to provide possible strategies for managing and minimizing the potential for significant injection-induced seismic events," EPA told NGI's Shale Daily. "Legal and policy considerations of Class II regulations are outside the scope of this draft technical report.
"EPA's Underground Injection Control program regulates injection of fluids related to oil and gas production as Class II injection wells for the protection of underground sources of drinking water. EPA does not have regulations specific to seismicity, but rather has discretionary authority that allows additional conditions to be added to Underground Injection Control permits on a case-by-case basis, as well as additional requirements for construction, corrective action, operation, monitoring, or reporting (including closure of the injection well) as necessary to protect underground sources of drinking water."
The agency is seeking input from technical experts in industry, academia and the U.S. Geological Survey on the draft report, which will also be available for public review and comment, EPA said.
Scientists have linked a dozen small earthquakes in the Barnett Shale in North Texas to wastewater injection wells that support natural gas drilling (see NGI, Aug. 13, 2012). Similarly, an injection well in northeastern Ohio was shut down in early 2012 after a dozen small earthquakes in the region. Arkansas banned disposal wells in a portion of the Fayetteville Shale after quake activity there. But scientists have disagreed over whether there is a relationship between hydraulic fracturing and earthquakes.
Researchers at Columbia University recently said earthquakes that occur on the other side of the world could create smaller temblors near wastewater injection sites in the United States (see NGI, July 15).
Disposal wells are hardly the first known human causes of earthquakes, according to the EPA draft report. "Others include construction of dams and water reservoirs, mining activities, oil and gas production and geothermal energy production," EPA said.
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