A GEOHYDRODYNAMIC STUDY OF THE ROLE OF FAULTS ON PETROLEUM MIGRATION IN THE CALIFORNIA BORDERLAND BASINS

We are applying newly-developed computational models to study the effects of Cenozoic extension, basin subsidence, transpression, and faulting on the migration of deep subsurface fluids (formation waters and petroleum) within the siliciclastic and petroleum-rich reservoirs of the California Borderlands, including the Santa Barbara and the Los Angeles basins. Subsurface geology, reservoir data, and structural-seismic sections provide a clear picture of the degree of apparent compartmentalization for these well-known, petroleum-rich fault networks in an active tectonic setting. These data also provide constraints for geohydrodynamic flow models that are being developed to forward model pore pressures, flow rates, reactive-flow patterns, effects of fault-based fluid mixing and mineralization, geothermics, and large-scale deformation. For example, we have constructed numerical simulations to characterize the fluid flow history of the Los Angeles basin for both single and two-phase fluid migration. The single-phase flow models are similar to those of Hayba and Bethke (1995), and simulate the basin-scale compaction-driven flow associated with deep-basin subsidence and later uplift of the San Gabriel Mountains. The two-phase flow models provide a more detailed resolution, showing the effects of the stratigraphy and structure, and do a robust job simulating patterns of petroleum migration associated with the southwestern basin margin where deep faults produced thick stacking of petroleum accumulation over multiple formations. Our model results suggest a long periods of episodic flows (100~200 kyr) from the deep depocenter towards the western flank of the LA basin and the Palos Verdes Peninsula. Computational experiments clearly strong effects of fault, the fluid physics being controlled by Peclet and Capillary Numbers. The models also predict a strong preference for focused flow and petroleum trapping along the Newport-Inglewood Fault Zone, but also substantial leakage across the NIFZ and other faults, to elevate petroleum saturations in the the siliciclastic reservoirs of the giant Wilmington field.