Coupling accumulation model with gas-bearing features to evaluate low-rank coalbed methane resource potential in the southern Junggar Basin, China

Abstract

To reveal the resource potential of low-rank coalbed methane (LRCBM) and determine the favorable area from six different zones in the southern Junggar Basin in China, a new LRCBM assessment methodology was developed. This methodology comprises three steps: developing the regional accumulation model, determining the zone with gas-bearing features, and exploring for the favorable targets. First, the coalbed methane (CBM)-generating characteristics, the sealing properties of the over-and underlying rocks in the CBM reservoir, and the hydrogeological characteristics preserved in the reservoir were analyzed. By combining these characteristics with the tectonic burial history, geothermal history, hydrocarbon evolution, and CBM gas-saturation changes, the LRCBM regional accumulation model that illustrates the LRCBM-enrichment characteristics of the Middle-Lower Jurassic series in the southern Junggar Basin was derived. Second, the LRCBM gas-bearing features of each zone were comprehensively analyzed using a large data set acquired from a coalfield; the LRCBM-bearing features and the variation of their related parameters in six different zones of the southern Junggar Basin were presented. These parameters relate to features such as coal-seam distribution, petrology, reservoir property, coal thermal evolution, and coal and gas content characteristics. Third, the favorable targets are explored by calculating the LRCBM resources and intensively evaluating each zone; the favorable targets are candidates for further exploration in the southern Junggar Basin. At depths shallower than 2000 m (similar to 7000 ft), the LRCBM resources in the southern Junggar Basin are 3054.7 x 10(8) m(3) (10.8 x 10(12) ft(3)), with resource abundance of (0.42-11.65) x 10(8) m(3)/km(2) ([0.06-1.66] x 10(8) ft(3)/ac), thereby demonstrating a significantly good exploitation prospect. Moreover, the favorable and relatively favorable areas for further exploration in the southern Junggar Basin are zone 4 and 5, respectively.