Impact of a century of reservoir operations on fault stability at the Wilmington Field, CA

Lluis Salo-Salgado, Josimar A. Silva, Julia Mansfield, Andreas Plesch, John H. Shaw, & Ruben Juanes

Published September 8, 2024, SCEC Contribution #13855, 2024 SCEC Annual Meeting Poster #040

Previous experience with fluid injection and production has exposed the hazard of induced seismicity, which can compromise the integrity of subsurface reservoirs and lead to economic and human loss. Managing this hazard is even more important in tectonically active settings, such as southern California, where major faults can host damaging earthquakes.
Here, we develop a coupled model of multiphase flow and geomechanics of the Wilmington oil field, the largest in the Los Angeles Basin, California. Since the 1930’s, there has been approximately 2.5 billion barrels of oil produced and ten times as much water injected in the field. This history, together with extensive structural and geophysical data of the basin, provides a unique opportunity to assess the long-term impacts of reservoir operations on seismic hazard. Specifically, we assess (1) the spatial extent of induced stress changes, and (2) the evolution of fault stability. Our flow-geomechanics model includes a detailed representation of 24 faults in and around the field, monthly production and injection history, and the effect of permanent (plastic) deformation.
During the first 30 years of production, the model is able to reproduce observed ground subsidence, and predicts stress changes several kilometers beyond the main producing interval. Significant pore pressure decline (>8 MPa, >1160 psi) stabilizes most portions of the tear faults crossing the main producing interval. However, several of these faults are also destabilized locally due to reservoir compaction and water injection toward the end of this period. Reservoir compaction also destabilizes the Wilmington Fault bounding the main producing interval. These effects suggest that subsurface gas injection and withdrawal (e.g., in the case of hydrogen) in similar settings may destabilize faults, and highlights the need for adequate monitoring protocols.

Key Words
coupled flow-geomechanics modeling, fault stability, reservoir production, hydrogen storage

Citation
Salo-Salgado, L., Silva, J. A., Mansfield, J., Plesch, A., Shaw, J. H., & Juanes, R. (2024, 09). Impact of a century of reservoir operations on fault stability at the Wilmington Field, CA. Poster Presentation at 2024 SCEC Annual Meeting.


Related Projects & Working Groups
Seismology