Rate-and-state modeling of injection-induced aseismic slip in the Delaware Basin

No'am Z. Dvory, Yuyun Yang, & Eric M. Dunham

Submitted August 16, 2021, SCEC Contribution #11648, 2021 SCEC Annual Meeting Poster #175

Fluids injection into the subsurface raises the pore pressure and may induce seismicity. However, in numerous sites, injection is not accompanied by earthquakes. Moreover, in some areas of active injection and seismicity, seismic slip alone can not explain the ground deformation that accompanies injection, raising the possibility of aseismic slip. One example of this comes from the Southern Delaware Basin, where large volumes of oilfield water has been injected into the arkose sandstone of the Delaware Mountain Group. Here, Pepin et al. (2021) used a 3D dislocation inversions of InSAR measurements to identify more than 20 cm asiesmic slip on shallow, conjugate normal faults, in addition to small earthquakes (M < 3.5). In the present study, we develop and calibrate a 2D coupled pore pressure diffusion and rate-state model with mildly velocity-strengthening friction. Pore pressure diffusion is limited to a high-permeability fault damage zone and our estimation of net fluid influx into the fault zone is approximately 1-100% of the volume injected in nearby disposal wells, with the percentage increasing in proportion to the assumed fault zone width. Our simulations show that 1-2 MPa pressure change is required to initiate slip on the normal faults in a critically stressed crust. Most aseismic slip occurs at approximately constant friction and ~5 MPa additional pressure rise is needed to reach ~20 cm slip. We also explore the impact of variation in the injection rate. In this particular geometry, the fault response to injection is almost instantaneous and slip stops and resumes in relation to the pore pressure rise and fall.

Key Words
Aseismic slip, Coupled pore pressure diffusion and rate-state friction model

Citation
Dvory, N. Z., Yang, Y., & Dunham, E. M. (2021, 08). Rate-and-state modeling of injection-induced aseismic slip in the Delaware Basin. Poster Presentation at 2021 SCEC Annual Meeting.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)