ABSTRACT: Characterization and Exploitation of the Distal Margin of a Slope-Basin Reservoir, Yowlumne Field, San Joaquin Basin, CA

CLARK, MICHAEL S.; JOHN D. MELVIN, and RICK K. PRATHER

Yowlumne is a giant oil field in the southern San Joaquin basin, CA which has produced over 100 MMBL of 30 degrees oil from the Stevens sandstone, a clastic facies of the Monterey Shale (Upper Miocene). Most Yowlumne production is from the Yowlumne sandstone, a fan-shaped, layered, prograding turbidite complex in the Stevens deposited in slope-basin settings. Well log, seismic, and pressure data indicate reservoir compartmentalization into seven depositional lobes with left-stepping geometries attributed to Coriolis forces, and basinward-stepping geometries attributed to decreasing accommodation and high sediment flux. Log-derived petrophysical data, constrained by core analyses, indicate trends in reservoir quality. Concentration of channel and lobe facies along the axis and west (left) margin of the fan results in amalgamated, clean sandstones with average net/gross sandstone of 80%, clay content (Vsh) of 6%, effective porosity (phi[eff]) of 16%, and liquid permeability (liquid) of 10-20 md. By contrast, more abundant levee and distal margin facies along the east side result in a higher frequency of interbedded, shale-bounded reservoir layers with higher clay contents (Vsh=12%), and lower net/gross (65%), phi[eff] (12%), and K[liquid] (2 md). Although a waterflood will enable recovery of 45% of original oil in place along the fan axis, a flow simulation model indicates that 3 MMBL of recoverable oil trapped at the thinning fan margins will be abandoned with the current well distribution. Economic recovery of this by-passed oil requires horizontal to high-angle deviated wells in which multiple fracture stimulations provide connectivity in a layered, low-permeability turbidite reservoir.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California