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Book Chapter

Abnormal Pressure in Hydrocarbon Environments

By
Ben E. Law
Ben E. Law
U.S. Geological Survey Denver, Colorado, U.S.A.
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C. W. Spencer
C. W. Spencer
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Published:
January 01, 1998

Abstract

Abnormal pressures, pressures above or below hydrostatic pressures, occur on all continents in a wide range of geological conditions. According to a survey of published literature on abnormal pressures, compaction disequilibrium and hydrocarbon generation are the two most commonly cited causes of abnormally high pressure in petroleum provinces. In young (Tertiary) deltaic sequences, compaction disequilibrium is the dominant cause of abnormal pressure. In older (pre-Tertiary) lithified rocks, hydrocarbon generation, aquathermal expansion, and tectonics are most often cited as the causes of abnormal pressure.

The association of abnormal pressures with hydrocarbon accumulations is statistically significant. Within abnormally pressured reservoirs, empirical evidence indicates that the bulk of economically recoverable oil and gas occurs in reservoirs with pressure gradients less than 0.75 psi/ft (17.4 kPa/m) and there is very little production potential from reservoirs that exceed 0.85 psi/ft (19.6 kPa/m). Abnormally pressured rocks are also commonly associated with unconventional gas accumulations where the pressuring phase is gas of either a thermal or microbial origin. In underpressured, thermally mature rocks, the affected reservoirs have most often experienced a significant cooling history and probably evolved from an originally overpressured system.

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Contents

AAPG Memoir

Abnormal Pressures in Hydrocarbon Environments

B.E. Law
B.E. Law
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G.F. Ulmishek
G.F. Ulmishek
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V.I. Slavin
V.I. Slavin
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American Association of Petroleum Geologists
Volume
70
ISBN electronic:
9781629810768
Publication date:
January 01, 1998

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