Application of Multivariate Statistics in Crude Quality Characterization and Regional Distribution in Orinoco Oil Belt
Published:January 01, 1987
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M. Taheri, N. M. de Audemard, 1987. "Application of Multivariate Statistics in Crude Quality Characterization and Regional Distribution in Orinoco Oil Belt", Exploration for Heavy Crude Oil and Natural Bitumen, Richard F. Meyer
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Today’s technology provides geochemists with numerous statistical techniques, helping them to manipulate, interpret, and deduce results from large amounts of data. Pairwise correlation coefficient and multivariate statistical methods of principal components and cluster analyses were applied to 14 physical and chemical properties of 288 crudes, in order to determine the qualities and their regional distribution patterns in the Orinoco Heavy Oil Belt of Eastern Venezuela.
The initial set of properties (API gravity; kinematic viscosity at 100°F, 140°F, and 210°F; V, Ni, and S content; gross composition; water and crude salinity; and yield below 370°C) were submitted to pairwise comparison and correlation, taking into account their importance in the processes of production, transportation, and refining. It was found that five characteristics (API gravity, kinematic viscosity, V, S, and asphaltene content) are sufficient to characterize the crude qualities in the belt.
Furthermore, the principal components and cluster analyses were applied to the assemblages of these five characteristics for 165 sample localities to classify them into four quality types: A, B, C, and D. Type A denotes the best quality with API gravities greater than 13°, kinematic viscosities at 210°F less than 60 cSt., and sulfur and vanadium contents less than 1.60% and 250 ppm, respectively. Type D represents the extra-heavy crudes with API gravities <8.5°, viscosities at 210°F >300 cSt., sulfur content >3.8%, and vanadium content >400 ppm. Based on this limited number of samples, it has been observed that 10% of the crudes are of Type A, 20% are of Type B, 35% are of Type C, and the remaining 35% are of Type D. These four groups were mapped to show their regional distribution in the entire belt.
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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.