Abstract
Oil and gas hydrocarbons are formed at temperatures above 100 °C by the chemical breakdown of the organic remains of dead organisms preserved in fine-grained rocks called source rocks. The organic remains are known as kerogen. If enough hydrocarbons are formed, some are expelled from the source rocks. We have analysed Kimmeridge Clay (Upper Jurassic) shales from the North Sea which are currently expelling hydrocarbons into adjacent sandstones. The results could be explained if most expulsion occurs by the pressure-driven flow of a discrete hydrocarbon phase through the pores of shales and into the pores of the sandstones, as suggested previously1. In addition, capillary forces seem to increase the efficiency of expulsion close to the interfaces between the shales and interbedded sandstones. It appears that molecular diffusion of hydrocarbons with less than about ten carbon atoms alters the composition of the hydrocarbon fluids remaining in, and expelled from, the shales.
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Mackenzie, A., Leythaeuser, D., Muller, P. et al. The movement of hydrocarbons in shales. Nature 331, 63–65 (1988). https://doi.org/10.1038/331063a0
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DOI: https://doi.org/10.1038/331063a0
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