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Book Chapter

The Mechanical Properties of Rock through an Ancient Transition Zone in the Appalachian Basin

By
Irene Meglis
Irene Meglis
The Pennsylvania State University University Park, Pennsylvania, U.S.A.
*
Present address: Queen's University, Kingston, Ontario, Canada.
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Terry Engelder
Terry Engelder
The Pennsylvania State University University Park, Pennsylvania, U.S.A.
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Published:
January 01, 1994

Abstract

Hydrostatic compression tests were used to measure the variation in mechanical properties of Devonian core cut through an ancient pressure transition zone in the Appalachian Plateau of western New York. The properties of this core are strongly influenced by low aspect ratio microcracks developed during stress relief. In the siltstones, linear compressibility decreases with increasing confining pressure to a minimum value between 14 and 16 x 10­6 MPa­1 in all directions. In the shales, linear compressibility parallel to bedding is approximately 10 x 10­6 MPa­1 for all confining pressures, but normal to bedding it decreases with increasing confining pressure throughout the range of test pressures (140 MPa), reaching minimum values between 25 and 40 x 10­6 MPa­1 at high pressure. The high linear compressibility normal to bedding reflects compression and closure of a dense population of bedding-parallel microcracks. Microcrack porosity is lowest in the core 50 m above the ancient transition zone and is higher further above and below the zone. In conclusion, rocks within the ancient transition zone have lower intrinsic compressibilities than overlying rocks (8-12 x 10­6 MPa­1 versus 9-18 x 10­6 MPa­1). Such a marked change in elastic properties near the transition zone may serve as a seismic reflector.

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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

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