Reservoir Performance Characterized in Mature Steam Pattern

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

A detailed reservoir description provided new insight in an investigation of a ten-year-old steam flood. Mobil Oil Corporation conducted this study of the Pleistocene upper Tulare sands in South Belridge field, located in the San Joaquin basin, Kern County, California. The study area is on the gently dipping (6°) southwestern flank of the South Belridge anticline. Wireline logs from 19 wells in a 10-ac (660 ft × 660 ft) pattern were correlated in detail. Seven post-steam conventional cores (1,523 ft) aided (1) the evaluation of vertical and lateral steam-sweep efficiency, (2) evaluation of reservoir and fluid changes due to steam, (3) influence of lithofacies in reservoir quality, and (4) provided insight to the three-dimensional reservoir flow-unit geometries.< P>

The upper Tulare unconsolidated reservoirs are mainly coarse to fine-grained moderately to poorly sorted arkosic sands deposited as coalesced channel-fill in an upper delta-plain setting. Recognized depositional subenvironments include (1) channels, (2) levees and crevasse-splays, and (3) overbank. Tulare reservoir sands exhibit excellent reservoir quality, with an average porosity of 36% and permeabilities (air) ranging from 100 to more than 10,000 md. Reservoir flow-unit geometries are distinguished from individual channel geometries using evidence of observed steam-flow patterns. The importance of noting steam distribution is emphasized by a 0% residual oil saturation after steaming. Steam-induced authigenic diagenesis of the immature mineralogy and alteration of the heavy 13° API oil has occurred in the reservoir.

Variations in reservoir permeability and fluid saturations are strongly influenced by depositional lithofacies, reflecting the absence of significant compaction and diagenesis. Reservoir flow-path tortuosity and fluid conformance to flow are better understood in this reservoir by considering the scale and orientation of reservoir heterogeneities relative to well spacing.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.