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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 33 (1949)

Issue: 12. (December)

First Page: 2063

Last Page: 2063

Title: Time of Oil and Gas Accumulation: ABSTRACT

Author(s): A. I. Levorsen

Article Type: Meeting abstract

Abstract:

An idea of the time oil and gas accumulated into pools may be gained through two separate and simple lines of reasoning. These are: (1) a pool can not form until after the trap has been formed. We have several methods of dating geologically the time the trap was formed and consequently setting the time or times before which there could have been little or no accumulation; and (2) the capacity of a trap to contain oil and gas is roughly a function of the pressure in the reservoir. The pressure in turn is related to the depth of burial and the hydrostatic head. Pools full of oil and gas to the spill point have accumulated only under the increasing pressure which comes with burial. Both types of reasoning support the idea that in some pools at least, the accumulation was lat in terms of the life of the reservoir rock--accumulation even taking place to the present time.

The PVT relationship of gases may also be used to explain the time of regional migration of oil and gas within basins and provinces. The drilling of a hole into an oil and gas pool, for example, allows the gas to expand as the pressure gradient develops between the pool and the well hole. The expanding gas moves toward the area of lower pressure, either carrying or pushing the oil along with it. Basins and other large geologic units have experienced numerous upsets of their PVT relationships during their history. Tilting, faulting, folding, regional arching, erosion, and deposition all serve to upset the PVT equilibrium from time to time. The development of a pressure gradient through such causes as these makes for the expansion and movement of gas toward the area of lower pressure in a manner similar to what we know exists when a well is drilled into a pool. The available energy may be very large. Local traps which existed prior to the regional movement would collect oil and gas into pools whereas local traps which formed after the regional movement would be barren.

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Copyright 1997 American Association of Petroleum Geologists