Thermal chromatography or pyrolysis-gas chromatography of mixtures of expanding three-layer clays and sedimentary organic matter or kerogen gives insight into the differences in composition of pyrolyzates of specific sediments and isolated kerogens. Argillaceous sediments containing less than about 2% kerogen-C yield pyrolyzates consisting primarily of low molecular weight hydrocarbons in the gas condensate range, whereas kerogens isolated from such sediments yield a broad range of hydrocarbons as in oil. Pyrolyzates of organic-rich sediments are similar in composition to pyrolyzates of isolated kerogens, being oil-like. The ratio of expanding three-layer (smectite) clays to organic matter in sediments apparently controls the degree of catalytic cracking, so that argillaceous sediments relatively low in organic matter yield low molecular weight hydrocarbons due to more carbon-carbon bond cleavage. Kerogens mixed with quartz, silica, alumina, calcium carbonate, kaolin, or illite yield pyrolyzates more similar to those of the respective kerogens alone. This is due ostensibly to a lack of catalytic activity of these minerals as compared with the catalytically active smectites. Smectitic argillaceous sediments that contain less than approximately 2% organic carbon are poor sources of oil, although they may be productive of gas and gas condensate. These observations are related to gas and gas condensates of the northern Gulf of Mexico basin and in Indonesia, and to oil in the North Sea area.

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