Poroelastic modeling of groundwater and hydrocarbon reservoirs : investigating the effects of fluid extraction on fault stability

Abstract

The possibility of human-triggered earthquakes is critical to understand for hazard mitigation. This project was developed to better understand the stability of faults in areas with high amounts of fluid extraction, and was applied to both a groundwater and hydrocarbon basin. The theory of poroelasticity was used to calculate the stress changes resulting from fluid flow. Then, the resulting fault stability was evaluated with the the Coulomb Failure Function ([Delta]CFF). A COMSOL and MATLAB workflow was used to derive the results. Two applications were completed. The primary research focused on the extraction from a groundwater aquifer in Lorca, Spain, in relation to the M, 5.1, 2011 earthquake. A smaller project was completed for the production of an oil well in Wheeler Ridge, California, in relation to the Mw 7.7, 1952 earthquake. In Lorca, it was found that extraction from a local aquifer promoted failure on an antithetic fault to the major Alhama de Murcia Fault. Specifically, while the left-lateral portion of the slip was stabilized, the reverse component of the slip was promoted (depth -5 km). Published InSAR and focal mechanism results support a rupture plane aligned with the antithetic fault. The final stress change was ~0.03 MPa which is small but not negligible compared to the expected total stress drop (~2 MPa). In California, the production from Well 85-29 was of interest. It was found that oil extraction promoted failure on the White Wolf Fault. There was a region adjacent to but below the reservoir that tended toward destabilization after the production. However, there was a notably small stress change (~0.5 kPA). This project lends to some important conclusions, and demonstrates that the poroelastic deformation of an aquifer or reservoir can result in distinct zones of stabilization and destabilization on pre-existing faults.