Significance of Reservoir Stratigraphy in Production of Heavy Oil from Coalinga Oil Field, California
Published:January 01, 1987
M. A. Bate, S. A. Graham, 1987. "Significance of Reservoir Stratigraphy in Production of Heavy Oil from Coalinga Oil Field, California", Exploration for Heavy Crude Oil and Natural Bitumen, Richard F. Meyer
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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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Exploration for Heavy Crude Oil and Natural Bitumen
Gross volumes of oil, which must be kept in mind to address the volume/size framework, may be thought of in order from largest to probably smallest volumes as follows: (1) generated; (2) dissipated; (3) degraded/ partially preserved; and (4) trapped and conventionally producible. Basic knowledge of these volumes may be from greatest to least in essentially reverse order.
The 332 largest known accumulations (less than 1% of the total number) account for more than three-quarters of the known 7.6 trillion bbl of oil and heavy oil or tar in more than 40,000 accumulations in the world. About 2.4 trillion bbl of estimated undiscovered conventional oil added to the known volume of 7.6 trillion bbl yields a total of 10 trillion bbl known or reasonably estimated. World-wide cumulative production of about 500 billion bbl of oil accounts for only 5% of the gross.
Oil in place must be estimated for conventional oil fields before comparison with heavy oil and tar accumulations. The size range of accumulations considered in the size distribution of the 332 largest known accumulations is from 0.8 to 1850 billion bbl of oil. The smallest conventional fields in the distribution are about 1 billion bbl because the size cut-off is 0.5 billion bbl of oil recoverable. The size distribution of the 332 largest known accumulations approaches log normal and is overwhelmed by the largest three supergiant tar deposits that hold nearly half of the total 5495 billion bbl.
Globally, the largest three accumulations, all heavy oil or tar, are in South and North America; the two largest conventional oil fields are in the Middle East. Prudhoe Bay and East Texas fields rank 18 and 34, respectively, in descending size order.