>Distribution and Occurrence of Metals in Heavy Crude Oils and Solid Bitumens— Implications for Petroleum Exploration
Published:January 01, 1987
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J. A. Curiale, 1987. ">Distribution and Occurrence of Metals in Heavy Crude Oils and Solid Bitumens— Implications for Petroleum Exploration", Exploration for Heavy Crude Oil and Natural Bitumen, Richard F. Meyer
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A world-wide suite of 82 crude oils and 21 solid bitumens was analyzed for concentrations of cadmium, chromium, cobalt, copper, iron, manganese, molybdenum, nickel, vanadium, and zinc. The oils analyzed are predominantly heavy oils, having a mean API gravity of 17.4° and a mean asphaltene content of 15.5%. Preliminary tests indicated that the metal content cannot be reduced by passing the oils through a 5 micron filter. For both the oil and solid bitumen data sets, vanadium, nickel, and iron are in highest concentration. The concentrations of nickel, cadmium, vanadium, chromium, and molybdenum show negative correlations with API gravity, although no correlation coefficients (r) are greater than 0.80. The remaining elemental concentrations show no correlation with either API gravity or asphaltene content. Mean metal concentrations in the solid bitumens are higher than those in the oils in every case. The consistent relationship between mean concentrations for the two groups suggests the existence of a genetic continuum containing conventional oils, heavy oils, and solid bitumens. These data are useful in a beginning effort to apply transition metal data to petroleum exploration efforts. Ultimately, metal data will be useful in predicting oil type and volume capable of generation from an oil source rock.
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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.