Oil Potential of Coals: A Geochemical Approach

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Abstract
Summary: Rock-Eval and pyrolysis GC data show that coals from various origins generate on thermal cracking up to 30% weight in form of hydrocarbons. Most of them consist of oil-type components (C 6 + hydrocarbons) up to about 1.5% vitrinite reflectance maturity. Therefore fair quantities of oil should be generated during maturation of such samples. Paradoxically, coal-rich sediments contain only minute amounts of oil, whatever their maturity rank. This is interpreted by an easy expulsion of hydrocarbons from coals during burial. Moreover, trapping of oil in the ‘microporosity’ of coals, or due to their ‘plastic’ behaviour is unlikely. Therefore coals should have a fair potential for oil generation and expulsion and the observed poor association between coal measures and oil pools is due to geological reasons rather than to geochemical ones. Distributions and yields of the generated hydrocarbons may be quite different from one sample to another. For instance, North Sea coals do not resemble coals from Tertiary deltas.