This work investigates structural styles and natural fracturing within the southern San Joaquin basin, California. The study area encompasses much of the western fold belt and ultimately focuses on the Buena Vista Hills oil field. We present an exploration methodology that integrates image analysis with potential field data and published surface geology. Regional geomorphic analysis identified major ENE-trending structures transecting a series of NW-trending folds and related thrust faults. ENE fractures developed into lateral ramps with oblique components of displacement during thrust-related folding. The ENE structures, together with the thrust faults, represent compartment-bounding faults.

Several structural compartments were identified over the Buena Vista Hills oil field. Surface fractures were mapped in each compartment using high-resolution image data; the resulting fracture location and orientation data suggest that flexural slip during folding is the driving mechanism for development of open fractures in the Buena Vista anticline. The structural compartments have impermeable boundaries that influence the reservoir system: cumulative production data from the Antelope Shale reservoir show that compartment boundaries limit and segment productive areas of the field. There exists evidence that gas production due to desorption occurs in the Monterey Formation, and that the potential for producing desorbed gas could be enormous. Exploiting the desorbed gas potential may rely on finding small reservoir compartments that have a better chance of reducing reservoir pressures by dewatering the formation.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah