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Book Chapter

Electric-Log Characteristics of Diapiric Shale1

By
J. A. Gilreath
J. A. Gilreath
New Orleans, Louisiana 70112
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Published:
January 01, 1968

Abstract

Diapiric shale along the Texas and Louisiana Gulf Coast is highly pressured and characteristically has low values of resistivity, density, and acoustic velocity, properties easily measurable by electrical logging. However, deep-water marine shale in normal stratigraphic positions also may be highly pressured and produce similar log characteristics. Therefore, although logs which reflect the above-mentioned parameters indicate that highly pressured shale has been penetrated, they do not indicate whether the shale is part of a diapiric mass or is in normal stratigraphic position.

Dip meter surveys provide information to establish whether or not the shale is intrusive. In addition, if the shale is found to be intrusive, dipmeter information locates the apex of the diapir with respect to the position of the well. As the shale diapir is approached from above, normal bedding-plane dips (away from the apex) increase in magnitude—just as if domal salt were being approached. After the low-resistivity shale is penetrated, the dips (cleavages?, flow surfaces?) are relatively constant in both magnitude and azimuth. These dips within the diapiric mass approximate the dip of the contact between the normally bedded strata and the diapiric shale. This consistent dip within the diapiric mass is very different from the random dips found in gouge shale adjacent to piercement salt domes.

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Contents

AAPG Memoir

Diapirism and Diapirs: a symposium

Jules Braunstein
Jules Braunstein
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Gerald D. O’Brien
Gerald D. O’Brien
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American Association of Petroleum Geologists
Volume
8
ISBN electronic:
9781629812304
Publication date:
January 01, 1968

GeoRef

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