Geology of Heavy Crude Oil and Natural Bitumen in the USSR, Mongolia, and China
Published:January 01, 1987
A. A. Meyerhoff, R. F. Meyer, 1987. "Geology of Heavy Crude Oil and Natural Bitumen in the USSR, Mongolia, and China", Exploration for Heavy Crude Oil and Natural Bitumen, Richard F. Meyer
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The USSR, Mongolia, and China occupy an area of 33,385,390 km2, or a quarter of the earth’s land area. Large reserves and resources of heavy crude oil and natural bitumen are present, especially on the Eastern European (Russian) and Siberian platforms, where at least 700 billion bbl is present (out of 1000 billion or more for the USSR as a whole). Chinese and Mongolian resources, in contrast, are of the order of 100 billion bbl. Thus, the heavy oil and natural bitumen reserves and resources of the Siberian platform comprise one of the three largest accumulations in the world, the other two being the Western Canada basin and the Eastern Venezuela basin. Most of the USSR reserves and resources are Paleozoic and Proterozoic, unlike those of most of the rest of the world, which are Mesozoic and Tertiary. Moreover, carbonate-platform deposits predominate, in contrast to the near-shore clastic environments common elsewhere.
Two lineages of heavy oil and bitumen are well developed. The first is the kir, or regressive lineage, characterized by the loss of the light fractions from a paraffinic or paraffinic-naphthenic parent oil and the formation of surface stratiform deposits, kirized bitumens, and asphalt lakes. Deposits of this lineage form in short periods of time, rarely longer than 10 million years. Kirs are found in active tectonic belts (e.g., mobile belts, active horst-and-graben areas, mud-volcano fields, etc.). The second, and quantitatively more important, platform or progressive lineage is characterized by thermal metamorphic changes during evolution and high concentrations of sulfur, nickel, vanadium, copper, uranium, and other elements derived from a largely naphthenic-aromatic parent oil. Such deposits form during time periods that usually exceed 100 million years. One apparent end product of platform-lineage bitumen development can be the creation of rich and economic concentrations of sedimentary, stratabound, metallic ore deposits.
Heavy-oil and bitumen deposits of platform lineage commonly are found in ancient mobile belts. In the Soviet Union and China, such deposits are found in several Paleozoic fold belts, especially in volcanic or eugeosynclinal facies. The presence of platform-lineage deposits in volcanic/eugeosynclinal belts commonly indicates that those strata are allochthonous. Thus, the presence of sizable heavy-oil and bitumen deposits in tectonized volcanic belts may provide a valuable clue to the identification of a major overthrust belt. Future exploration programs for normal petroleum accumulations must take into account the possible significance of heavy-oil and natural bitumen deposits in incompatible geochemical settings.
Figures & Tables
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.