C. M. Isaacs, 1987. "Sources and Deposition of Organic Matter in the Monterey Formation, South-Central Coastal Basins of California", Exploration for Heavy Crude Oil and Natural Bitumen, Richard F. Meyer
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The abundant organic matter in the Monterey Formation is commonly considered to be derived from marine algal debris rapidly deposited in anoxic bottom water during a period of high surface plankton productivity. However, many aspects of the distribution of organic matter in the Monterey of the south-central coastal basins are inconsistent with this view. For example, organic matter is generally most abundant in beds representing lowest (not highest) surface plankton productivity and slowest (not fastest) organic-matter accumulation. Moreover, at least in the Santa Barbara coastal area, organic matter is generally most abundant in beds representing intermediate (not lowest) bottom-water oxygen. The one expected relation that generally holds true is that organic matter is most abundant in beds with the smallest original grain size.
The distribution of organic matter in the Monterey Formation of the south-central coastal basins raises several questions about the source and depositional environment of this organic matter. For example, is the organic matter really mainly marine in origin, is it generally a mixture of marine and terrigenous debris, or does the mixture vary from basin to basin? How important is oxygen level in bottom water to preservation of organic matter? What other environmental conditions are important in determining the abundance and character of preserved organic matter? Review of present-day environments thought to be analogous to the depositional setting of the Monterey Formation shows that the distribution of organic matter in these environments is also complex and only partly understood. Thus, depositional and early diagenetic controls on Monterey organic matter should be thoroughly reexamined.
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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.