Abstract The Permian Basin has experienced 9,900 ML 2.0+ earthquakes since 2017 due to the re-injection of produced water from ~35,000 horizontal wells into strata above (shallow-salt water disposal SWD) and below (deep-SWD) shale production intervals. Curtailment of deep-SWD within regulated seismic response areas (SRAs) has resulted in declined monthly rates since 2021; however, in the Northern Culberson Reeves SRA (NCR SRA), seismicity rates have remained high despite curtailment of deep-SWD, and this has caused ongoing concern. There are three distinct levels of faulting identified within a ~1,500 km2 3D seismic reflection dataset: i) intra-basement (IB); ii) basement-rooted (BR); and iii) shallow, strata-bound faults (SSB). IB are low-to moderate-angle (~20–45°) Proterozoic thrust faults, which are truncated by the Great Unconformity. BR faults are moderate-to high-angle reverse and subvertical strike-slip faults (~50–90°), which offset the Great Unconformity and overlying Paleozoic strata including deep-SWD injection strata. SSB are steeply-dipping (~60–80°) elongate, narrow graben, which deform upper-Permian age units, including shallow-SWD injection strata. We apply a regional stress model, which reflects a normal faulting regime and fault slip sensitivity is assessed using Coulomb shear failure model. Under these conditions, most SSB faults are optimally oriented for slip, BR faults range from stable to critical, and IB faults are stable, requiring significant pore pressure increase to reach criticality. In the NCR SRA, significant earthquakes (ML 4.0+) are located exclusively within the basement. These events are spatially linked to BR fault segments, which sole into IB imbricate faults and extend into deep-SWD injection strata, providing direct hydraulic communication between faults and SWD injection intervals.
Horne et al. (Thu,) studied this question.