Coring and Sampling in Heavy-Oil Exploration: Difficulties and Proposed Cures
Published:January 01, 1987
M. B. Dusseault, J. D. Scott, 1987. "Coring and Sampling in Heavy-Oil Exploration: Difficulties and Proposed Cures", Exploration for Heavy Crude Oil and Natural Bitumen, Richard F. Meyer
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Core samples of friable heavy-oil sands are invariably damaged due to irreversible expansion caused by gas evolution. This expansion has a major impact on property determination, particularly for flow parameters and geomechanical properties. Sample quality can be significantly improved by following a number of simple guidelines and by implementing a few improvements on existing equipment. The major factor is provision of physical restraint on core to prevent expansion. It is always necessary to implement a program to determine the degree of sample disturbance, so that the effects of mitigating activity can be quantified. Also, the goal for sampling for parameter assessment should not be quantity, but quality: One meter of superb quality core is preferred to 100 m of expanded core.
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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.