EARTHQUAKES INDUCED BY HYDRAULIC FRACTURING ARE PERVASIVE IN OKLAHOMA

Wastewater disposal is generally accepted to be the primary cause of the increased seismicity rate in Oklahoma within the past decade, but no statewide analysis has analyzed the contribution of hydraulic fracturing (HF) to the observed seismicity or the seismic hazard. We collected all available information on timing and location of HF in Oklahoma in the past decade to evaluate their relationship to seismicity. Utilizing an enhanced seismicity catalog generated with multi-station template matching from 2010-2016, we identified ~300 HF wells that are spatiotemporally correlated with bursts of seismicity. We were guided to these sequences by calculating a delta earthquake rate for all HF wells based on seismicity before, during, and after the reported stimulation interval, and then sorting wells to focus on those with the largest increase in seismicity rate during stimulation. We identified 16 regions showing multiple cases where bursts of seismicity are linked to specific HF stimulations. Although the majority of cases occurred throughout the SCOOP/STACK play, we also identified prominent cases in the Arkoma basin as well as some more complex potential cases along the edge of the Anadarko Platform. The spatial distribution of correlated cases suggests that the proximity of basement faults plays a role in where HF-induced seismicity occurs. For HF treatments where we have access to injection parameters, modeling suggests poroelastic stresses are likely responsible for seismicity, but pore pressure may still be a contributing factor.

In all of the 16 regions we identified, ≥75% of the seismicity from 2010-2016 correlated with reported HF wells. In some regions, >95% of seismicity correlated with HF wells and >50% of the HF wells correlated with seismicity. Overall we found ~700 HF-induced earthquakes with M≥2.0, including 12 with M≥3, and a maximum magnitude of 3.5. These findings imply state regulations implemented in 2018 that require operators in the SCOOP/STACK play to take action if a M > 2 earthquake occurs are likely to have a significant impact on future operations.