Abstract

As part of a global study to evaluate the contribution of coals to the petroleum resource base, thermally immature coals from Sumatra, Java, Kalimantan, Australia, and New Ireland were analyzed to determine: 1) hydrocarbon generation potential; 2) organic matter composition; 3) anticipated products; and 4) ability to expel generated hydrocarbons.

Our results indicate that there is considerable variation in the ability of coals to generate hydrocarbons. The observed differences are greater than can be explained by the variation in organic enrichment. A major controlling factor is the availability of organic hydrogen. Kerogen atomic hydrogen to carbon ratios ranged from approximately 0.6 to greater than 1.6.

The nature of potential products, as determined by pyrolysis-gas chromatography, also displays substantial variability. The products of alginite-dominated coals are largely paraffinic and waxy. Vitrinite-rich coals yielded more aromatic products than the alginite-dominated coals. Coals containing significant amounts of resinite yielded important quantities of naphtheno-aromatic compounds.

Although the question of petroleum expulsion from coals is difficult to address in the laboratory, the data indicate that the saturation of the coal pore network cannot readily be achieved, thus preventing oil expulsion. High molecular weight compounds appeared to be retained and cracked to gas at higher vitrinite reflectance values. An exception may be coals similar to the Australian torbanite where hydrocarbon generation may be sufficient to achieve pore network saturation.

The results of this study indicate that coals generally do not contribute to the petroleum resource base. An exception may be algal-dominated coals. These coals are, however, volumetrically limited.