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ABSTRACT: Production of Tectonically Caused Overpressures in Carbonates by Using Resistivity and Bulk Density of Associated Shales

G. V. Chilingarian, Walter H. Fertl

In tectonically caused overpressured carbonate reservoirs associated with thick shale beds (e.g., 50 m and more), several shale properties can be used as predictive techniques: low porosities, high acoustic (sonic) velocities, high resistivities, and high bulk densities. The reason these properties are used is because the greater the degree of overcompaction (due to tectonic forces), the greater the amount of water squeezed from the shales, which, in turn, overpressures the

associated reservoirs. Two case studies from the Soviet Union and Iran illustrate this occurrence.

For comparison purposes, the prediction of overpressures caused by undercompaction (e.g., due to rapid sedimentation) using conventional overpressure indicators, such as resistivity, acoustic and density logs, and bulk density of shale cuttings, are reviewed and illustrated via a typical Tertiary sand/shale sequence.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990