Geomechanical analysis of fluid injection and seismic fault slip for theM_w4.8 Timpson, Texas, earthquake sequence

Abstract

An earthquake sequence that culminated in a Mw4.8 strike‐slip event near Timpson, east Texas, the largest reported earthquake to date in that region, had previously been attributed to wastewater injection starting 17 months before the onset of recorded seismic activity. To test if this earthquake sequence can be attributed to wastewater injection, we conducted coupled poroelastic finite element simulations to assess the spatial and temporal evolution of pore pressure and stress field in the vicinity of the injection wells and to calculate the Coulomb failure stress on the seismogenic fault as a function of the permeability of the injection layer, fault orientation, fault permeability, and orientation and magnitude of the in situ stress. We find that injection‐induced fault slip is plausible within the range of selected model input parameters, with slip favored by low reservoir permeability, low fault permeability, and a favorable orientation of the fault relative to the in situ stress state. Other combinations of equally plausible input parameters predict no slip within 96 months of simulated injection. Under most favorable boundary conditions for fault slip, fault slip occurs 7 months after the start of injection. Our results highlight the importance of detailed geomechanical site characterization for robust fault stability assessment prior to wastewater injection.

A Historical Review of Induced Earthquakes in Texas

“…A search of records at station NATX in Nacogdoches (about 35 km distant) revealed that several small earthquakes, apparently from the same focus, had occurred in 2008, 2010, and 2011 (Frohlich et al, 2014), and subsequent reanalysis of Transportable Array data revealed additional earthquakes that occurred between 2010 and 2012 (Walter et al, 2016). Fan et al (2016) simulated the spatial and temporal evolution of the pore pressure and stress fields in this region using a coupled finite-element geomechan-▴ Figure 11. Earthquakes, injection wells, and production wells at the Dallas-Fort Worth (DFW) International Airport.…”

State of stress in Texas: Implications for induced seismicity

“…In addition, both moment tensors were subsequently recalculated on 23 June 2016 using a more refined local velocity model [see Herrmann, 2016], resulting in two strike-slip focal mechanisms with similar nodal plane and P axis orientations to one another (Figure 2d). Fan et al [2016] demonstrate that poroelastic stress changes could allow P P to build to the point that a severely misoriented fault could slip, but a requirement of their model is that no well-oriented faults are present. At the~2.5 km top-fault depth shown by Frohlich et al [2014], only 1.8-6.8 MPa ΔP P in the case of the 17 June 2012 M w 4.8 earthquake and 0.7-2.7 MPa ΔP P for the 10 June 2012 M w 3.8 earthquake were needed to trigger slip (Table 1).…”

Fluid Injection and Time‐Dependent Seismic Hazard in the Barnett Shale, Texas

“…Most studies addressing the correlation between injection and nearby seismicity either are qualitative (Ake et al, 2005;Frohlich, 2012) or quantify pore pressure using uncoupled groundwater flow equations Keranen et al, 2014). Recent studies consider coupling between pore pressure and matrix deformation to investigate the relationship between injection and earthquakes (Deng et al, 2016;Fan et al, 2016;Segall & Lu, 2015;Shirzaei et al, 2016). This relationship is a function of injection rate, local hydrogeology, initial pore pressure and background stress state, fault orientation and permeability, and frictional properties (Chang & Segall, 2016;Fan et al, 2016).…”