Catalytic effect of smectite clays in hydrocarbon generation revealed by pyrolysis-gas chromatography

Temperature-programmed pyrolysis-gas chromatography of mixtures of expanding three-layer clays and Eocene Green River Formation kerogen gives insight into the differences in composition of pyrolyzates of specific sediments and of isolated kerogens. Argillaceous sediments containing less than about 2τ total organic carbon yield pyrolyzates containing primarily low molecular weight hydrocarbons in the gas condensate range whereas kerogens isolate from such sediments yield a broad range of volatile products including higher molecular weight hydrocarbons. Pyrolyzates of organic-rich sediments are much more similar in composition to pyrolyzates of isolate kerogens. The ration of expanding three-layer clays to organic matter in sediments apparently controls the degree of catalytic cracking so that argillaceous sediments relatively low in organic matter yield volatiles rich in low molecular weight hydrocarbons due to more carbon—carbon bond cleavage. These observations are related to gas and gas condensates of the northern Gulf Mexico basin and in Indonesia and to oil in the North Sea area.