Surface Deformation and Induced Seismicity Due to Fluid Injection and Oil and...
Texas is experiencing increasing seismicity, likely related to the oil and gas production process. We used satellite InSAR (Interferometric Synthetic Aperture Radar) to monitor surface deformation at three study sites in western Texas with similar geologic characteristics. The deformation data were compared to earthquake distribution, groundwater changes, volumes of produced and injected fluid, and calculated pore pressure change and Coulomb failure stress change to assess causes of deformation and seismicity. Site 1 experienced surface uplift due to fluid injection but no increase in seismicity. The average media properties were estimated based on the deformation using a poroelastic model. Site 2 experienced subtle surface subsidence and elevated seismicity. Subsidence here might reflect groundwater withdrawal. Simulated pore pressure changes using MODFLOW suggest the earthquakes are likely induced by fluid injection. Site 3 experienced significant surface subsidence and seismicity. InSAR time series, water level data, and oil/gas extraction history suggest that subsidence in the northern part of this site reflects oil/gas extraction, while subsidence in the southern part is mainly due to groundwater withdrawal. An Okada tensile model was used to derive the equivalent source strength causing the subsidence, then Coulomb failure stress changes associated with this source were calculated. We found that pore pressure change (simulated using MODFLOW) due to fluid injection is likely the main contributor to elevated seismicity at this site. Variations in oil/gas production activity, seismicity, and surface deformation between our three sites suggest the importance of local rock structure and media properties in determining susceptibility to induced seismicity. Plain Language Summary In recent years, both oil/gas production and earthquake number have increased in western Texas. This coincidence suggests at least some of the earthquakes are likely related to the oil/gas production process. We used sequential satellite images to measure surface deformation at three study sites in the Delaware Basin, western Texas. These three sites show different patterns of surface deformation and earthquake occurrence: (1) Site 1 has obvious uplift but no earthquakes; (2) Site 2 has little subsidence but many earthquakes; (3) Site 3 has significant subsidence and earthquakes. By analyzing temporal and spatial correlations between multiple independent data sets and the results of numerical models, we found the likely causes of the deformation and elevated earthquakes: (1) Surface uplift at Site 1 is due to fluid injection; (2) surface subsidence and earthquakes at Site 2 are probably related to groundwater withdrawal and fluid injection, respectively; and (3) the obvious surface subsidence at Site 3 reflects groundwater withdrawal in the south and oil/gas extraction in the north, while earthquakes are likely related to fluid injection. Since our model results rely on subsurface media properties, better assessment of whether an earthquake was or was not induced will require better knowledge of local rock properties.