Widespread deep seismicity in the Delaware Basin, Texas, is mainly driven by shallow wastewater injection

Abstract

Industrial activity away from plate boundaries can induce earthquakes and has evolved into a global issue. Much of the induced seismicity in the United States' midcontinent is attributed to a direct pressure increase from deep wastewater disposal. This mechanism is not applicable where deep basement faults are hydraulically isolated from shallow injection aquifers, leading to a debate about the mechanisms for induced seismicity. Here, we compile industrial, seismic, geodetic, and geological data within the Delaware Basin, western Texas, and calculate stress and pressure changes at seismogenic depth using a coupled poroelastic model. We show that the widespread deep seismicity is mainly driven by shallow wastewater injection through the transmission of poroelastic stresses assuming that unfractured shales are hydraulic barriers over decadal time scales. A zone of seismic quiescence to the north, where injection-induced stress changes would promote seismicity, suggests a regional tectonic control on the occurrence of induced earthquakes. Comparing the poroelastic responses from injection and extraction operations, we find that the basement stress is most sensitive to shallow reservoir hydrogeological parameters, particularly hydraulic diffusivity. These results demonstrate that intraplate seismicity can be caused by shallow human activities that poroelastically perturb stresses at hydraulically isolated seismogenic depths, with impacts on seismicity that are preconditioned by regional tectonics.

Keywords: hydrocarbon recovery; induced seismicity; wastewater.

Fig. 1.

Industrial and seismic activities within the Delaware Basin, TX. (A) Map and cross-section views of the spatial distributions of disposal wells, production wells, and declustered original TexNet earthquakes with foreshocks and aftershocks removed. The earthquake and well depths in the layered model are corrected relative to the Delaware sandstone formation bottom as a vertical reference (SI Appendix, SI Text). Black lines are the county boundaries. Black triangle indicates the location of the town of Pecos. (Inset) The location of the study area. (B) Temporal evolution of recorded injection and production volumes and four different declustered catalogs within the study area. The catalogs include the original TexNet catalog and improved TexNet and ANSS catalogs made by template matching (14) and TXAR catalog (13).

Fig. 2.

Cumulative total CFS from poroelastic stresses and pore pressure at seismogenic depth (5 km) within the basement during 2014 to 2020. (A) CFS for shallow sandstone injection. (B) CFS for deep Ellenberger injection. (C) CFS for shale extraction. (D) The sum of A–C. Dark curves show the faults. Blue squares show the well locations for the corresponding well types. Purple circles indicate the declustered TexNet earthquake epicenters.

Fig. 3.

Deformation map showing the distribution of SAR LOS velocity between 2016 and 2020. Red and blue colors indicate the surface movement toward and away from the satellite, respectively. (Inset) The footprint of the PV aquifer as well as the study area. Magenta curve shows the seismic quiescence zone following Fig. 2 and SI Appendix, Fig. S2. Yellow and gray curves are the approximate zones of the shallow water table and thick alluvial deposit in PV, respectively (41). Squares indicate the well locations, with symbol sizes scaled by average monthly well volumes during the same observation period as the deformation.

Fig. 4.

Schematic summarizing the physical processes associated with fluid injection and extraction. Injection in the shallow disposal layer, characterized by smaller hydraulic diffusivity, causes larger extensional poroelastic response within the basement. Extraction in the fractured shale, characterized by larger hydraulic diffusivity, causes smaller compressional poroelastic response within the basement. The basement and unfractured shale share similar poroelastic processes due to fluid injection and extraction. Fluid pathways connecting the shallow disposal layer and deep basement may locally increase the basement fluid pressure.