Fluvial-Deltaic Heavy Oil Reservoir, San Joaquin Basin

Donald D. Miller, John G. McPherson, Thomas E. Convington

Unconsolidated arkosic sands deposited in a fluvial-deltaic geologic setting comprise the heavy oil (13° API gravity) reservoir at South Belridge field. The field is located along the western side of the San Joaquin basin in Kern County, California. More than 6,000 closely spaced and shallow wells are the key to producing the estimated 1 billion bbl of ultimate recoverable oil production. Thousands of layered and laterally discontinuous reservoir sands produce from the Pleistocene Tulare Formation. The small scale of reservoir geometries is exploited by a high well density, required for optimal heavy oil production. Wells are typically spaced 200-500 ft (66-164 m) apart and drilled to 1,000 ft (328 m) deep in the 14-mi² (36-km²) producing area. uccessful in-situ combustion, cyclic steaming, and steamflood projects have benefited from the shallow-depth, thick, layered sands, which exhibit excellent reservoir quality. The fundamental criterion for finding another South Belridge field is to realize the extraordinary development potential of shallow, heavy oil reservoirs, even when an unspectacular discovery well is drilled.

The trap is a combination of structural and stratigraphic mechanisms plus influence from unconventional fluid-level and tar-seal traps. The depositional model is interpreted as a braid delta sequence that prograded from the nearby basin-margin highlands. A detailed fluvial-deltaic sedimentologic model establishes close correlation between depositional lithofacies, reservoir geometries, reservoir quality, and heavy oil producibility. Typical porosity is 35% and permeability is 3,000 md.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.