Carbon dioxide-rich coals of the Oaky Creek area, central Bowen Basin: a natural analogue for carbon sequestration in coal systems

• Published in: Australian journal of earth sciences 2013-02, Vol.60 (1), p.125-140
• Main Authors: Golding, S. D., Uysal, I. T., Bolhar, R., Boreham, C. J., Dawson, G. K. W., Baublys, K. A., Esterle, J. S.
• Format: Article
• Language: English
• Subjects: Bowen Basin; Carbon capture and storage; Carbon dioxide; Carbon sequestration; Carbonates; Clay; clay mineralogy; Clay minerals; Coal; Coal mines; coal seam gas; coal systems; Coastal inlets; Creeks; Fluids; geosequestration; Hydrothermal activity; Isotopes; Kaolinite; Low temperature; Methane; Methanogenesis; Microorganisms; Mineralogy; Minerals; Mudstone; Organic matter; Radiogenic materials; Rb-Sr geochronology; Sandstone; Seams; Siderite; Stable isotopes; Storage; Triassic
• ISSN: 0812-0099; 1440-0952
• DOI: 10.1080/08120099.2012.750627

High-CO 2 -containing coal seams in the Oaky Creek area of the Bowen Basin, eastern Australia provide natural analogues of the processes likely to occur as a result of CO 2 injection and storage in coal systems. We conducted mineralogical, stable and radiogenic isotope and major element analyses of mudstones and sandstones adjacent to the coal seams and stable isotope and compositional studies of coal seam gas desorbed from the coals to establish the impact of the high CO 2 levels and the mechanisms that keep the CO 2 naturally sequestered. Siderite is the earliest carbonate phase present and occurs with kaolinite in mudstones and sandstones. It is interpreted to have formed under low-temperature, reducing conditions where methanogenesis has produced residual 13 C-enriched CO 2 . Enhanced kaolinite concentrations adjacent to a low-CO 2 -containing coal seam reflect interaction with acidic fluids produced during the coalification of organic matter. Stable isotope data for carbonates and Rb-Sr isochron ages for illitic clays indicate that illitic clay-carbonate assemblages adjacent to both coal seams formed as a result of meteoric hydrothermal activity in the Upper Triassic with more intensive mineralogical reactions evident in the high-CO 2 coals. The present-day CO 2 in the high-CO 2 coals at Oaky Creek was emplaced in the Upper Triassic based on dating of illitic clay minerals from the high-CO 2 well and is magmatic or deep crustal in origin. Methane in the coals is of mixed origin, with secondary biogenic CH 4 formed by microbial reduction of CO 2 predominant in the high-CO 2 coals. This suggests that methanogenesis may provide an additional sequestration mechanism for CO 2 in coal seams.