Abstract

The amount of carbon dioxide in elastic rocks in sedimentary basins increases with depth. Organic matter, dissolved organic species, and dissolution of carbonate minerals have been suggested as sources of CO2, which increases in abundance with depth and temperature. Isotopic compositions of aqueous HCO-3, gaseous CO2 and calcite from conventional hydrocarbon wells and steam-assisted recovery of heavy oil suggest that calcite, or other carbonate minerals, are the source of CO2, particularly at higher temperatures. Detailed examination of the stability of diagenetic minerals such as kaolinite, smectite, and analcime, among others, relative to the coexisting waters, indicates that silicate hydrolysis is the driving force for dissolution of carbonate minerals and the ultimate source of abundant CO2 in elastic rocks in diagenetic environments at temperatures over approximately 100 °C.

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