Delineation of Gas Sands by Seismic Stratigraphy in the Pericocal Area, Orinoco Heavy Oil Belt, Venezuela
Published:January 01, 1987
J. Licheri, N. Parra, 1987. "Delineation of Gas Sands by Seismic Stratigraphy in the Pericocal Area, Orinoco Heavy Oil Belt, Venezuela", Exploration for Heavy Crude Oil and Natural Bitumen, Richard F. Meyer
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The purpose of this study is to define the extent of gas sand bodies found in the Oficina Formation by well SDZ-79X, in the Pericocal area of the Orinoco Heavy Oil Belt.
True amplitude processing was applied to 30 km (19 mi) of seismic survey lines in the vicinity of this well. The processing showed amplitude anomalies on lines ZB-5, SC-B, and PE-2, produced by the interfaces between the relatively low-velocity gas sands and the high-velocity lignites and shales.
A model generated from the sonic log of well SDZ-79X was used in order to recognize the gas sands on the seismic section. The pinch outs of the sand bodies were located by the decrease of high amplitudes. Stacking velocities from the seismic, and average velocities from the surrounding wells, shows the existence of a low- velocity anomaly typical of gas accumulations, thereby confirming the zone of high-amplitude anomalies.
As a final result, three isopach maps of the gas sands were prepared, and a volume of 34 billion ft3 of gas in place was estimated.
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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.