Internal Structure of Turbidite Channel-Fill Reservoir and Its Effect on Oil Recovery, Yowlumne Field, California

Robert R. Berg, Gilberto R. Royo

The upper Miocene Yowlumne reservoir sandstones are channel-fill turbidites that contain complexly layered and lensing flow units at an average depth of 11,000 ft (3,353 m). The reservoir has a maximum thickness of 300 ft (91 m) and forms a channel-like body that ranges from 1 to 2 mi (1.6 to 3.2 km) wide and is 3 mi (4.8 km) long. The reservoir consists of six members that are bounded by shales and composed of thin beds that are 1-4 ft (0.3-1.2 m) thick separated by thin shales. Stratigraphic interpretation of the internal structure of the reservoir was made to predict oil recovery during both primary and secondary recovery.

Dip-log patterns suggest that the members contain overlapping, arcuate lenses that resemble longitudinal bars deposited within braided channels. Composite bars are channel-form flow units on the order of 50 ft (15 m) thick and 1,000 ft (305 m) wide, and their restricted lateral extent controls oil recovery. During primary production, the flow units are only partly drained, and infill wells within 40-ac spacing can produce water-free oil from isolated beds. During water flooding, the sweep is strongly controlled by the arcuate flow units, and water-oil ratios clearly show that injected water follows a curvilinear path between injection and production wells. It is concluded that the most efficient drainage of the reservoir will be from infill wells following the water flood.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.