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Book Chapter

Sesimic Amplitute Versus Offset (AVO) Character of Geopressured Transition Zones

By
John N. Louie
John N. Louie
The University of Nevada Reno, Nevada, U.S.A.
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Abu M. Asad
Abu M. Asad
The University of Nevada Reno, Nevada, U.S.A.
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Published:
January 01, 1994

Abstract

The presence of diagenetically cemented seals distinguishes between possible mechanisms for the maintenance of abnormal fluid pressures in sedimentary basins. The velocity gradients and Poisson’s ratio variations surrounding a cemented seal affect the pre-stack amplitude versus offset behavior of seismic reflections from the seal. Acoustic synthetic seismograms based on well logs from sealed transitions demonstrate their unusual AVO character. A long-offset COCORP reflection line near Port Lavaca, Texas, shows similar effects from a seal at 6000 ft (1800 m) depth. Local conductivity logs and regional drilling mud weight compilations establish the presence of this pressure transition zone. It is associated with a strong, low-frequency reflector near its base and displays linear AVO trends markedly stronger than from deeper reflections within the overpressured compartment. The fact that a seal exhibits such prominent physical property characteristics suggests that AVO analysis techniques may locate other seals in basins worldwide, where proper conditions for diagenetic sealing rather than shaliness and subsidence may be needed to maintain geopressures.

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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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