L. Horvitz, 1987. "A Geochemical Survey in the Santa Barbara Channel and Its Relationship to Subsurface Heavy-Oil Deposits", Exploration for Heavy Crude Oil and Natural Bitumen, Richard F. Meyer
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A geochemical survey was conducted in a part of the Santa Barbara Channel that contains three oil fields: Hondo, Pescado, and Sacate. The fields, especially Hondo, contain substantial reserves of low-gravity oil (14-26° API) in the fractured Monterey Formation of middle Miocene age.
The light hydrocarbons, methane through pentane, produced relatively weak and incomplete near-surface anomalies over the three oil fields. These results are to be expected considering the low gas-oil ratios in the reservoirs. The most outstanding anomalies were produced by aromatic compounds detected in the sediments about 1.8 m (6 ft) below the water-sediment interface. These compounds, probably consisting of naphthalenes and phenanthrenes and present in appreciable amounts in most crude oils, were measured by fluorescence techniques.
Carbon isotope ratios of adsorbed methane extracted from the fine-grained portions of the shallow sediments were also determined. Most of the δ13C1 values range from —40 to —49 parts per mil (PDB) and are indicative of an oil-prone area. Furthermore, the isotope ratio data produced anomalies over and adjacent to the oil fields.
When the geochemical data are compared with the known subsurface geology, close relationships are seen. Particularly striking similarities between the carbon isotope ratios, the heavier aromatic hydrocarbon fraction (fluorescence 365), and the geological data are apparent.
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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.