碳酸盐岩生油岩的有机地球化学、岩石学特征

ORGANIC GEOCHEMICAL AND PETROLOGICAL CHARACTERISTICS OF CARBONATE ROCKS AS A SOURCE ROCK FOR PETROLEUM

Features of oil-generating carbonate rocks are studied in terms of petrology and organic geochemistry of fluorescent materials in rocks. It is postulated by the authors that the organic carbon content in oil-generatlng carbonate rocks is necessarily lower than that in shales, and the possible cause of this observation is discussed. The quality of oil-ganerating carbonate rocks may be judged by aromatic structure index,amino acid, pigment index, and DTA data on organic matter. However, the application of presently available organic geochemical criteria to non-oil-generating reservoir rocks may always give misleading results. To circumvent this difficulty, it is necessary first to make distinction between primary and secondary organic matter by cxamining the fluorescent materials under a fluorescence microscope. Measurementof radical content of the organic substances and DTA are useful techniques to determine the degree of maturation. The maturation of organic substances proceeds at a lower rate in carbonate rocks than in shales. It is likely, therefore, that some older carbonate strata can also be promising areas for petroleum exploration. Oil-generating carbonate rocks consist mainly of mierite limestones rich in organic matter and are thought to be formed under low-encrgy environment. Consequently, petrological(especially mierolithofacies) studies are very important in evaluating carbonate source rocks.

Features of oil-generating carbonate rocks are studied in terms of petrology and organic geochemistry of fluorescent materials in rocks. It is postulated by the authors that the organic carbon content in oil-generating carbonate rocks is necessarily lower than that in shales, and the possible cause of this observation is discussed. The quality of oil-generating carbonate rocks may be judged by aromatic structure index, amino acid, pigment index, and DTA data on organic matter. However, the appli-cation of presently available organic geochemical criteria to non-oil-generating reser-voir rocks may always give misleading results. To circumvent this difficulty, it is necessary first to make distinction between primary and secondary organic matter by examining the fluorescent materials under a fluorescence microscope. Measurement of radical content of the organic substances and DTA are useful techniques to deter-mine the degree of maturation. The maturation of organic substances proceeds at a lower rate in carbonate rocks than in shales. It is likely, therefore, that some older carbonate strata can also be promising areas for petroleum exploration. Oil-gene-rating carbonate rocks consist mainly of micrite limestones rich in organic matter and are thought to be formed under low-energy environment. Consequently, petrological (especially mierolithofacies) studies are very important in evaluating carbonate source rocks.