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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 64 (1980)

Issue: 9. (September)

First Page: 1555

Last Page: 1556

Title: Reservoir Quality, Pliocene-Pleistocene Sandstones, Offshore Gulf of Mexico: ABSTRACT

Author(s): David K. Davies, William R. Almon

Article Type: Meeting abstract


Significant variations in the quality of sandstone reservoirs commonly reflect the amount of clay content which is controlled by the environment of deposition and diagenesis.

In the Pliocene-Pleistocene sandstones, offshore Gulf of Mexico, the clay content varies significantly between sands deposited in delta and submarine fan environments. The overall shapes of the gamma ray and SP curves for both environments are commonly similar,

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but differences between high and low resistivities can reflect differences in original environment of sand deposition.

Diagenesis can add significant quantities of clay to a rock through chemical precipitation in pore spaces. Diagenetic (authigenic) clays are of importance because they can significantly effect electric-log response (SP, gamma ray, neutron, density), and can largely control the reaction of a sand reservoir to well-bore fluids. It is often forgotten that diagenesis can also remove clays from a sandstone, thereby "cleaning-up" an originally dirty sandstone.

The composition of drilling and stimulation fluids also has a significant effect on reservoir quality, especially when the sandstone pores are lined with diagenetic clays. Use of incorrect drilling or stimulation fluids can make a potentially good reservoir nonproductive.

In the Pliocene-Pleistocene section of the Gulf of Mexico, variations in environment of deposition, diagenesis, and the composition of drilling fluids can play havoc with interpretations based solely on log characteristics.

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Copyright 1997 American Association of Petroleum Geologists