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Geological Society, London, Special Publications; 1987; v. 36; p. 15-28;
DOI: 10.1144/GSL.SP.1987.036.01.03
© 1987 Geological Society of London

Diagenetic Processes

Some aspects of diagenetic sulphate-hydrocarbon redox reactions

H. G. Machel

Basin Research Institute, Louisiana State University, Baton Rouge, Louisiana 70803-4101, USA
Department of Geology, University of Alberta, Edmonton, Alberta T6G 2E3, Canada

Sulphate-hydrocarbon redox-reactions occur at two specific diagenetic temperature/thermal maturity levels: less than about 75–85°C (0.2–0.3% R0), and more than 100–140°C (> 1.5% R0), respectively. In low-temperature/maturity environments these redox reactions take place only with the mediation of bacteria. In high-temperature/maturity environments these reactions take place thermochemically, and certain catalysts must interact in order to overcome the high activation energies and to sustain the reactions at geologically significant rates.

The reaction products and by-products may be identical for both temperature/maturity levels: altered and oxidized hydrocarbons (including bitumen), hydrogen sulphide, metal sulphides (including Mississippi Valley Type deposits), elemental sulphur, carbonates (mainly calcite and dolomite), and other minerals. An important by-product of these redox reactions may be porosity resulting from the dissolution of solid sulphates and/or the carbonate host rock. The net reaction is exothermic, and the released heat may generate a geothermal hot-spot in some cases.





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