Reactivation of Precambrian Faults by Deep Wastewater Injection in Midland Basin, Texas, and Performance Evaluation of Seismic Response Areas

Fluid injection associated with oil field operations can induce earthquakes through perturbation to the balance between fault strength and tectonic stress. Induced seismicity generally does not respond immediately to changes in injection due to time-delayed diffusion of pressure and heterogeneous prestress conditions on seismogenic faults. After exploitation for over a century without significant seismicity, the Midland basin experienced a rapid increase in activity since mid-2020, including events as large as an ML 5.2 with many felt throughout the Midland and Odessa metropolitan area. In response to societal and industry concerns, the Texas Railroad Commission established Seismic Response Areas around Stanton and Gardendale, to address the possibility that deep wastewater disposal was triggering earthquakes. In this study, we present a detailed earthquake catalog covering 2020 and 2021 for the Midland basin derived from regional and private seismic network data. Hypocenters are computed using a velocity model calibrated with sonic logs. We compare the location and timing of seismicity with development, production, and disposal operations. Seismicity predominantly occurs within the Precambrian basement deeper than wastewater disposal and oil production. Faults delineated by relocated seismicity are optimally oriented for failure in the tectonic stress field, and their focal mechanisms are consistent with the inferred fault geometries. Neither the onset of seismicity nor the occurrence of large events correlates directly in time with hydraulic fracturing or changes in deep injection. Rather, faults appear to activate in response to cumulative deep disposal. However, we suspect that both pore pressure diffusion from deep disposal and remote poroelastic stress changes associated with fluid injection and extraction influence the recent increase in seismicity in the Midland basin. In either case, the regulation of deep wastewater injection in the seismic response areas has the potential to reduce the seismic hazard in the Midland basin.