Geohydrology of Faults & Petroleum Migration, Los Angeles Basin, California

Large-scale faults, which can be fluid conduits or barriers (or both), can induce significant subsurface changes in pressure, effective stress, temperature, and chemical-reaction gradients that ultimately control patterns of diagenesis, mineralization, and fluid migration/seal formation. For example, basement structure and faulting exert strong controls on fluid migration within Los Angeles basin, a late Cenozoic pull-apart basin formed by irregular rifting, plate rotation, and transpressive shortening within the Tranverse Ranges/San Andreas transform boundary. The Newport-Inglewood fault zone (NIFZ) forms the southwestern basin boundary, and major petroleum fields are aligned with this boundary. Igneous rocks associated with the northern end of the NIFZ appear to have caused significant diagenetic and thermal effects on the reservoir sands. Thermal transients within local boreholes indicate a potentially active and very transient geohydrologic regime.

We are using finite element models to first characterize the regional-scale geohydrology, and understand how petroleum migrates from source rock to reservoir trap on the western side of the Los Angeles basin. Specifically we are interested on how the opening/closing of faults influence large-scale fluid migration patterns and rates, fluid pressure, and heat flow within the basin. Secondly, we are developing smaller-scale flow models to better understand the role of transient geohydrologic changes, to evaluate the effect of the NIFZ on local heat flow, and characterize structural controls on clastic diagenesis near the fault. In addition, we have built a two-phase flow model that can predict migration patterns of petroleum in the deep subsurface as an immediate response to the opening/closing of NIFZ. Ultimately we hope to couple these separate-flow models with chemical reactions and predict patterns and timing of diagenetic alteration along faults in a transpressive basin environment.