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Book Chapter

Summary of Published Literature on Anomalous Pressures: Implications for the Study of Pressure Compartments

By
Randi S. Martinsen
Randi S. Martinsen
University of Wyoming Laramie, Wyoming, U.S.A.
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Published:
January 01, 1994

Abstract

The phenomenon of anomalous geopressure has been a focus of study for almost 40 years. Until recently, most studies were concerned with either the detection of overpressure or with the processes by which anomalous pressure is generated. Two processes, disequilibrium compaction and hydrocarbon generation/maturation, probably account for the majority of overpressured rocks observed worldwide. Because anomalous pressure is often associated with undercompacted rocks, various techniques based on detecting under-compaction (in addition to formation pressure tests) are commonly used to detect anomalous pressure indirectly. Whereas formation pressure tests can only be obtained in porous and permeable reservoir-type rocks, indirect techniques can only be applied in thick shale sequences. Therefore, data sets obtained by these two different approaches are mutually exclusive.

There has been a great deal of uncertainty with regard to the existence and nature of pressure seals. Overall, researchers studying anomalous pressure fall into one of two categories: those who accept the existence of effective seals and those who do not. Researchers who do not believe seals exist support classic hydrologic interpretations that suggest anomalous pressures are bounded by low-hydraulic-conductivity rocks and are, therefore, geologically ephemeral. Those who do believe seals exist, for the most part, do not present specific evidence of what comprises a seal. Although the sealing capacity of various rocks for hydrocarbon accumulations has been investigated, very little research has been conducted specifically concerning the seals that contain anomalous pressures. The influence of capillary forces on hydrocarbon entrapment is widely recognized, but capillary phenomena have largely been ignored in studies dealing with geopressures, even though hydrocarbon generation is commonly cited as the mechanism by which overpressure is generated. The delineation of pressure compartments, especially those of known geologic duration, is an important tool by which potential seals can be mapped and investigated. Without specific knowledge of seal characteristics, well-founded interpretations of seal effectiveness and pressure compartment longevity cannot be made.

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Contents

AAPG Memoir

Basin Compartments and Seals

Peter J. Ortoleva
Peter J. Ortoleva
Department of Chemistry Indiana University Bloomington, Indiana
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American Association of Petroleum Geologists
Volume
61
ISBN electronic:
9781629810935
Publication date:
January 01, 1994

GeoRef

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