Do shallow injection wells contribute to the triggering of the 2020 M5.0
Mentone earthquake in the Delaware Basin, Texas?
Abstract
The M5.0 earthquake that occurred in March 2020 near the town of Mentone
in the Delaware Basin, Texas, is one of the largest induced earthquakes
recorded in the central US. A former study shows that the triggering of
this event can be attributed to the nearby deep injection.
Interestingly, the shallow injection wells in this region have an
injection volume five times larger than that of deep injection wells. In
this study, we investigate the role of these shallow injection wells in
the triggering of the M5.0 event despite their farther distance from the
mainshock. By performing focal mechanism inversion and earthquake
relocation, we determine the precise orientation of the south-facing
normal fault plane where the mainshock occurred, followed by fully
coupled poroelastic stress modeling of the change of Coulomb Failure
Stress (ΔCFS) on the fitted fault plane due to the shallow injection in
the region. Results show that shallow wells may cause up to 30 kPa of
ΔCFS near the mainshock location, dominated by positive poroelastic
stress change. Such perturbation surpasses the general triggering
threshold of faults that are well aligned with the local stress field
and suggests a nonnegligible role of these shallow injection in the
triggering of the mainshock. Our study also highlights the effect of
rock properties of injection layers on the magnitude and spatial extent
of pore pressure and stress perturbations, supporting the importance of
detailed geomechanical evaluation of the reservoir when developing
relevant operational and safety policies.