2020 M5 Mentone earthquake potentially induced by deep wastewater injection: implications for reservoir mechanical property and individual well impacts

Abstract:

The M5 quake that occurred on March 26, 2020, in the Delaware Basin of West Texas, the US largest petroleum-producing area, was the most significant event that happened within the past two decades. There are eight nearby class-II wells, injecting wastewater into the deep Ellenburger aquifer at an average rate of 1.36x10⁶ BBL/mo since 2012, while the seismicity rate started deviating from the background rate in 2017. We used a coupled poroelastic model to simulate the injection-induced transients of crustal stresses and pore pressure and evaluate how the Coulomb failure stress was built up at the M5 quake location. We find that the deep injection wells, depending on injection rate and distance, have a distinct contribution in the evolution of the Coulomb stress at the M5 fault. Two deep injections at 10 and 20 km distance to the epicenter, imparted 18.3 and 45.0 kPa of Coulomb stress increase, respectively. This suggests that only a single remote injector is capable of inducing the earthquake, assuming a triggering threshold of 10 kPa. Two additional wells farther away (26-30 km) jointly contributing a smaller but non-negligible Coulomb stress increase of 10.4 kPa. In general, we found the triggering effect from each well decays with the inverse square of its distance to the epicenter, i.e., doubling the well-fault distance results in a ~80% reduction in Coulomb stress change. The long-range poroelastic effect and individual impacts from these wells are proved significant over a broad range of aquifer permeability of 10^-14 through 10^-12 m² supported by previous studies. Through a nonlinear Monte Carlo search, we find that an intermediately permeable reservoir of permeability 6.76x10^-14 m² provided the most favorable stress condition for the M5 rupture to occur at the peak of pore pressure changes in early 2020, i.e., a year after the regional injection rate reached its maximum. Overall, this study reveals indicative poroelastic models and spatiotemporal relations between deep injection wells and the earthquake fault, providing insights into hazard mitigation and industrial management of disposal operations.