Geomechanical Analysis of Fluid Injection and Seismic Fault Slip for the M4.8 Timpson, Texas, Earthquake

Abstract

An earthquake sequence that culminated in a MW4.8 strike-slip event near Timpson, east Texas, the largest documented earthquake to date in that region, had previously been attributed to waste water injection starting 69 months prior to the main seismic event. To assess the geomechanical relationships between fluid injection and seismic fault slip, we created a coupled poroelastic finite element model to simulate the spatial and temporal evolution of pore pressure and stress field in the vicinity of the injection wells and of the Coulomb failure stress on the fault as a function of the permeability of the injection layer, fault orientation, fault permeability, and orientation and magnitude of the in situ stress state prior to injection. We find that fault slip is favored by low reservoir permeability, low fault permeability, and a favorable orientation of the fault relative to the in situ stress state. We also demonstrate that sensitivity of the Coulomb failure stress to variations in input parameters results in large uncertainties in correlating injection rate and volume with the onset of induced seismic events. Using a plausible but narrow range of input parameters, we simulate the onset of fault slip to occur as early as 7 months after injection, to no seismic event within 96 months of simulated injection.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016