Regulators and researchers in Oklahoma, anticipating a major increase in oil and gas drilling in the state's stacked reservoirs, have jointly developed new seismicity guidelines intended to reduce the risk of earthquakes.
The Oklahoma Corporation Commission (OCC) said its Oil and Gas Conservation Division (OGCD) developed the guidelines with the Oklahoma Geological Survey (OGS) to cover the Midcontinent reservoirs -- specifically, the South Central Oklahoma Oil Province (SCOOP) and the Sooner Trend of the Anadarko Basin in Canadian and Kingfisher counties (STACK).
Oklahoma regulators have been trying to mitigate induced seismic activity across the state, especially from wastewater injection wells targeting the Arbuckle formation, for nearly two years. According to OGCD Director Tim Baker, operations in the Mississippian Lime and the Hunton Dewatering play -- which lie within a 15,000-square-mile area of interest (AOI) -- produced an unprecedented amount of saltwater, which is reinjected into disposal wells.
But Baker said there is one bit of good news: the SCOOP and STACK plays aren't capable of generating large amounts of wastewater.
"There is broad agreement among researchers that disposal of these large amounts of water into the state's deepest formation [the Arbuckle] can be linked to the high earthquake rate in parts of the AOI," Baker said Tuesday. "By comparison, the SCOOP and STACK plays have very small amounts of produced water."
OGS Director Jeremy Boak said the new seismicity guidelines for the stacked plays were developed using both old and new data. He said research conducted years ago by then-state seismologist Austin Holland revealed some small earthquakes in the SCOOP and STACK areas may have been related to hydraulic fracturing (fracking) activities.
"More recent small events outside the AOI might also be linked to fracking," Boak said. "While the data indicates that seismicity related to the SCOOP and STACK would be far less frequent and much lower in magnitude than the activity we are addressing in the main earthquake region of the state that has been linked to wastewater disposal, we have enough information to develop a plan aimed at reducing the risk of these smaller events as operations commence."
The new guidelines call for three courses of action, depending upon the magnitude of the earthquake, for wells conducting fracking operations that are also located within two kilometers (1.25 miles) of seismic activity.
Under the first scenario, where OGS has determined that an earthquake of 2.5 magnitude or greater has occurred, the OGCD will contact operators with active completion operations and direct them to implement the operator's internal mitigation practices. The well will be allowed to continue operating.
If the earthquake measures 3.0 magnitude or greater, operations will be paused for no less than six hours, during which time a technical conference or call will be held between OGCD staff and the well's operators to discuss the latter's mitigation practices. Upon agreement between the operator and the OGCD, operations will be allowed to resume with a revised completion procedure.
Operators will be required to suspend operations if an earthquake measuring 3.5 magnitude or greater strikes within 1.25 miles of the well. An in-person technical conference between OGCD staff the well's operators will follow to determine in operations can resume with changes.
Baker and Boak emphasized that state regulators remain focused on the AOI as the source for any strong magnitude earthquakes.
"Unlike the strong earthquake activity in areas of the AOI linked to disposal activity, response to seismic activity that might be related to hydraulic fracturing can be more precisely defined and rapidly implemented," Boak said.
Researchers from Stanford University recently reported that the number of earthquakes measuring 3.0 magnitude or greater near wastewater injection wells should decline over the next few years.
The OGCD began ordering operators to either shut down or curtail intake volumes at injection wells in March 2015, shortly before scientists with the OGS attributed the increase in seismic activity to injection wells targeting the Arbuckle, which closely overlies the crystalline basement. The OGS said the disposal of extremely salty water -- a byproduct of oil and gas production, not the mostly freshwater used for fracking -- is responsible for the quakes.