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Abstract

The Miocene Temblor Formation is a prolific producer of heavy crude oil at Coalinga oil field in central California, having produced nearly 700 million barrels of 20° API oil from the lower part of the formation from 1900 through 1981. In Coalinga field and other nearby fields, the Temblor Formation often produces from multiple, discrete intervals. Primary lenticularity of reservoir stratigraphy suggested by this production history was further demonstrated by qualitative log-shape mapping of one Temblor interval published by Shell Oil geologists in the 1970s. These data indicate that optimum efficiency in production from steam soak and steam drive demands full knowledge of the fabric of the Temblor reservoir.Outcrop studies indicate that the lower Temblor Formation of the Coalinga area represents fluvial deposits left by southerly flowing braided streams, overlain by transgressive lagoonal and shallow-marine deposits. This record can also be recognized in the subsurface nearby, where depositional trends have been mapped using a “resistivity factor” that takes into account interval thickness and magnitude of resistivity response. The method works well for lower Temblor units where only porosity and oil-water saturation vary appreciably among petrophyscial factors. The maps produced show good correlation between depositional trends and concentrations of oil, within an individual depositional unit. Recognition of these units and their lateral anisotropy aids efficient recovery of heavy oil from the reservoir.

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