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Regulators in Oklahoma say data gathered since seismicity guidelines went into effect in late 2016 supports new requirements for oil and gas operators planning to drill in the state's stacked reservoirs, thereby reducing the chances of future earthquakes from completion activities.
On Tuesday, the Oklahoma Corporation Commission (OCC) and its Oil and Gas Conservation Division (OGCD) issued a directive outlining a new seismicity protocol for oil and gas operations in the SCOOP (the South Central Oklahoma Oil Province) and STACK (the Sooner Trend of the Anadarko Basin in Canadian and Kingfisher counties), which account for the majority of new oil and gas activity in the state.
OGCD Director Tim Baker said the oil and gas industry fully cooperated with the previous protocol issued in December 2016, but that data gathered since then support taking additional measures.
"The overall induced earthquake rate has decreased over the past year, but the number of felt earthquakes that may be linked to well completion activity, including hydraulic fracturing, in the SCOOP and STACK has increased," Baker said Tuesday. "These events are relatively rare and smaller on average than those linked to injection activity.
"Most importantly, the risk of such events appears to be manageable. Learning how to mitigate the risk of causing such events is an ongoing process. The changes we are announcing today are part of that process."
Under the new protocol, all oil and gas operators working within a 15,000-square mile area of interest (AOI) in the stacked plays will be required to certify to the OGCD that it has adopted a seismicity response plan related to any potential seismic activity within a five-kilometer (3.1-mile) radius of completion operations. Operators conducting hydraulic fracturing (fracking) will also be required to have access to a seismic array that provides real-time seismicity readings.
The minimum level at which an operator must take action was lowered from 2.5 to 2.0 magnitude. Regulators said that, in general, the minimum level at which an earthquake can be felt is a 2.5 magnitude.
The new protocol also stipulates that drillers will be required to pause their operations for six hours following a temblor measuring at least 2.5 magnitude, during which time they would participate in a technical conference call with regulators. Under the previous protocol, the minimum level requiring a pause was 3.0 magnitude.
For temblors measuring at least 3.0 magnitude but less than 3.5, operators would face the additional step of agreeing with OGCD staff on appropriate mitigation measures before activities are allowed to resume, albeit under revised procedures. Operations must be immediately suspended following temblors measuring 3.5 magnitude or greater. An in-person technical conference with operators and OGCD staff would be held to examine whether operations can resume with changes.
Baker said data gathered over the past year indicates earlier action may be best. "While more study needs to be done, the indications are that those operators who have their own seismic arrays and took actions when there were seismic events too small to be felt decreased the risk of having multiple, stronger earthquakes," he said.
Oklahoma Geological Survey (OGS) Director Jeremy Boak concurred, but added that the new protocol should be considered as a next step in the process of mitigating induced seismic activity.
"Ultimately, the goal is to have enough information to develop plans that will virtually eliminate the risk of a felt earthquake from a well completion operation in the SCOOP and STACK," Boak said.
The OCC and OGCD have been attempting to mitigate induced seismic activity across the state since at least 2015. They have focused on wastewater injection wells targeting the Arbuckle -- especially the Mississippian Lime and the Hunton Dewatering play -- within the 15,000-square mile AOI. Scientists with the OGS attribute much of the seismic activity to the disposal of extremely salty water, a byproduct of oil and gas production, via underground injection wells.
State seismologist Jake Walter said Oklahoma could further reduce the risk of strong earthquakes from wastewater injection by upgrading OGS's existing seismic network to provide data 24 hours a day. Currently, the OGS network detects temblors measuring 2.0-2.5 magnitude across the state, and an analyst provides verification during normal business hours, except for larger events.
"The cost associated with expanding the seismic network would be a relatively small investment that would help to ensure the safe development of Oklahoma's billions of dollars worth of oil and natural gas," Walter said. "When coupled with other data on oil and gas activities that we hope will be forthcoming, we could develop a framework that would enable operators to know before they commence operations just what the estimated seismicity risk could be, what steps to take beforehand, and what to do during operations to minimize seismic hazards.
"As we speak, such mitigation efforts are being implemented by operators in the SCOOP/STACK. The sharing of the resulting data with OGS will help us to learn exactly what works."
Baker, Boak and Walter agreed that the threat of induced earthquakes from well completion activity is much smaller than the threat linked to injection of oil and gas wastewater in the north-central part of the state, where the larger and more frequent earthquakes have occurred.
"Production within the [AOI] resulted in an unprecedented amount of salt water which was already in the formation coming up with the oil and natural gas," Baker said. "That produced water was put back underground using disposal wells. There is broad agreement among researchers that disposal of these large amounts of water into the Arbuckle, the state's deepest formation, can be linked to the high earthquake rate we saw in recent years within parts of the AOI.
"By comparison, the SCOOP and STACK plays have very small amounts of produced water and whatever earthquake activity there is tends to be much smaller. We currently estimate less than 4% of detectable, induced earthquake activity in Oklahoma can be linked to fracking, and of that, an even smaller percentage can be felt."
Baker added that while the earthquake rate in the AOI has been dropping since limits on disposal were put in place, disposal into the Arbuckle within the AOI is still a concern.