Physical and Chemical Characterization of Heavy Crude Oil in the Orinoco Oil Belt
Published:January 01, 1987
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N. de Audemard, M. L. Chirinos, I. Layrisse, 1987. "Physical and Chemical Characterization of Heavy Crude Oil in the Orinoco Oil Belt", Exploration for Heavy Crude Oil and Natural Bitumen, Richard F. Meyer
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During the last 5 years, an exploration program was carried out in the Orinoco Heavy Oil Belt, located in eastern Venezuela. Over 600 wells were drilled and evaluated in order to quantify the reserves and to obtain information about the crudes accumulated in the 54,000 km2 (20,850 mi2) area of the belt.
Physical and chemical properties of more than 300 crudes were determined. Analysis of these data shows that crudes in the eastern part are different from those in the western part of the belt. Kinematic viscosity is dependent on API gravity in the eastern part, to the extent that a variation of 1° could correspond to up to one order of magnitude change in viscosity. The rest of the properties are interrelated, except gross oil composition; this is attributed to the severe alteration that affects most of the oils in the area. There is no clear-cut dependence among the properties of crudes from the western part owing to the low gravities involved <10°API). These crudes, however, present less alteration.
A set of 13 properties was correlated, but it was found that only five were required to describe the quality of the crudes: API gravity, viscosity, vanadium, sulfur, and asphaltenes content. Thus, representative crudes for the area can be defined.
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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.