Efforts to manage the potential risk for oilfield activity-induced earthquakes in Oklahoma are starting to pay off, state geological and regulatory officials said Tuesday, while acknowledging that additional research is needed for what is a continuing conundrum.
One of the early results points to some smaller, shallower seismic activity tied to well completions, but it is lower risk compared to injection-induced activity.
Oklahoma Geologic Survey (OGS) Director Jeremy Boak reiterated that wastewater disposal and not hydraulic fracturing (fracking) is the main culprit in some Arbuckle injection wells under scrutiny.
OGS and the Oklahoma Corporation Commission (OCC) reported the results of their collaborative efforts undertaken since late last year to establish well completion seismicity protocols for responding to quakes with magnitudes of 2.5 to 3.5-plus.
OCC has contacted operators on 27 events of 2.5 magnitude or more as reported by OGS. Events occurred within about 2 kilometers of a well completion operation, with specific mitigation actions undertaken by the operators.
The still-evolving, jointly developed "traffic light" protocol system has yielded positive results already, said OGS and OCC officials.
"The actions taken under the directive have been in response to events that have occurred away from the Arbuckle injection wells that have been linked to most of the quake activity in the state," said OCC’s Tim Baker, oil and division director. He said research has tied some of the smaller, relatively rare activity outside of the main quake area to well completion operations, including fracking.
Boak and State Seismologist Jacob Walter said the preliminary evidence suggests that the seismicity associated with well completions is "stratigraphically shallower" than quakes linked to deep injection and "does not appear to reactivate basement faults, unlike the more numerous and often far larger quakes linked to injection."
Boak said that current data indicates "wastewater disposal into the Arbuckle group -- not hydraulic fracturing operations -- poses the highest risk when it comes to induced earthquake activity."
The OCC ordered 50 wastewater injection wells near Cushing, a major oil hub, to either cease or scale back operations after a magnitude-5.0 quake struck. In March, the OCC ordered more than 400 injection wells targeting the Arbuckle to cut volumes by 40% below 2014 levels.
Last year Stanford University researchers said the number of quakes with magnitudes of 3.0 or more near Oklahoma’s oil and gas disposal wells should continue to decline over the next few years as a result of state's actions reducing wastewater injection volumes.