Wastewater Injection, Surface Deformation and Induced Earthquakes in Delaware Basin, West Texas

Disposing of the wastewater from fossil fuel production can perturb the state of stress through the fluid diffusion process, inducing seismic and aseismic slip on faults in proximity to the injection zones. Fault reactivation depends on several factors, including inhomogeneities in the hydrogeological properties, injection history, fault density, and fault slip sensitivity. The Delaware Basin of far west Texas was exploited in the 20th century using conventional vertical drilling. Horizontal drilling and hydraulic fracturing have also been deployed in this region since the 2009 which significantly increased hydrocarbon production. During the last decade, there has been a significant increase in earthquakes in Delaware Basin. To more closely study the causes of this rising seismicity rate, we examine pore fluid pressure change data from 2015 to 2020 due to wastewater injection and hydrocarbon extraction. We employed a one-way coupled approach through a finite element poroelastic simulator to quantify the ground surface displacement and stress changes on the surrounding faults, accounting for 3D heterogeneities of hydrological properties in the area. We simulated a continuous medium and postprocessed the stress concentrations to predict the most probable locations of soil failure. We find that the widespread seismicity and aseismic fault slips are likely promoted by stress change imparted due to wastewater disposal and hydrocarbon extraction. In particular, propagation of poroelastic stresses to hydraulically disconnected layers is the primary driver of some shallow seismic and aseismic fault slip and deflection of the ground surfaces. Future work will concern the explicit modeling of faults and the fully-coupled simulation of displacement and pressure fields.