Abstract

The Tulare reservoirs at South Belridge field clearly reflect the influences of both the regional tectonism of the active margin setting, and the numerous sedimentologic controls intrinsic to the depositional system. The large structure of the South Belridge anticline overprints hundreds of discontinuous reservoir sands to create a combination structural and stratigraphic trap. This is well documented by more than 6,100 active wells in the heavy-oil producing field. This giant oil field is projected to produce more than a billion barrels of oil, from shallow (400–1,400 ft) Plio-Pleistocene fluviodeltaic sands in a situation where the average daily production is less than 50 barrels per well.

The overall depositional setting of the Tulare at South Belridge field is that of a prograding fluviodeltaic system. Depositional environments include lacustrine, deltaic, and meandering and braided fluvial systems, with six major lithofacies types recognized. The sand-body geometries show considerable variability throughout the Tulare as a function of the changing character of the depositional system. Reservoir quality (permeability and oil saturation) and producibility are directly related to depositional lithofacies. Reservoir flow-unit geometries and quality can be predicted from the depositional model.