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Abstract: Authigenic Chlorite as a Controlling Factor in the Exploration of Turonian/Coniacian Turbidites in the Santos Basin

Ernani Porsche, Eduardo Lopes De Freitas

Upper Turonian/Coniacian and Campanian turbidites are major targets for petroleum exploration in the Santos Basin, southeastern Brazil. They occur between 140 and 1000 m of present water depth, are buried at about 4500 m, and reach thickness of up to 60 m.

The main reservoir facies is composed of unstratified, fine to very fine grained, poorly sorted sandstones, which framework is compositionally immature, including a high proportion of feldspars and volcanic rock fragments. Early coating of grains by authigenic chlorite inhibited pressure solution and quartz cementation in the reservoir. This diagenetic characteristic allowed important preservation of primary porosity (>20%) in the reservoir; nevertheless its permeability never exceeds 30 mD.

The study of sedimentary facies and related depositional processes has been conducted to predict the distribution of petroleum-bearing turbidites throughout the Santos Basin; this comprises a major challenge for the petroleum exploration in this important Brazilian exploration frontier.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela