ABSTRACT: Reservoir Delineation Using 3-D Seismic: Stevens Sands, Southern San Joaquin Basin, California

James H. Ligon, Steven L. Parks

The San Emidio Nose and Rio Viejo fields are located 20 miles south of Bakersfield in the southern San Joaquin Valley. The fields are situated on the east-plunging San Emidio nose and have produced 16 million bbl of oil out of middle Miocene Stevens sandstones. The reservoirs were deposited as coalesced basin-floor fans and contain numerous separately pressured sands. Delineation of both the fans and the internal sands, by integrating geophysical, geological, and engineering data, is key to exploring for similar stratigraphic oil accumulations.

The seismic data is very responsive to the increase in thickness of the total Stevens interval when the sand-rich fans are present and can be identified on the excellent quality three-dimensional seismic that covers the area. Separation between fans can be mapped by using seismic facies characterization, isochore, and amplitude distribution maps. However, limits of seismic resolution prevent the mapping of individual sands within the fans.

Geologic correlations suggest that the fans are aggregations of individual sands, with shales as thin as 3 ft providing effective seals. Sand distribution was mapped using electric logs, fluid contacts, and reservoir pressure data. The sands are shingled and appear to prograde from southeast to northwest. On a larger scale, the fans also appear to prograde in a similar manner.

Integration of geophysical, geological, and engineering data has furthered our understanding of Stevens oil accumulations in this area. Additional opportunities have been located, several of which are being tested.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990