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This study assesses the displacement of coalbed methane by CO 2 migration along a fault into the coal seam in the Yaojie coalfield. Coal and gas samples were collected continuously at various distances in NO.2 coal seam from F19 fault. Vitrinite reflectance, maceral, and pore distributions and proximate analysis of fourteen coal samples were performed. Gas components, concentrations, carbon isotopes of 28 gas samples were determined. We examined the coal-gas trace characteristics of coalbed methane displaced away from the fault by CO 2 injection after geological ages. From east to west, away from the F19 fault, the CO 2 concentration decreased, whereas the CH 4 concentration increased gradually. The d 13 C values for CO 2 varied between À9.94& and 1.12&, suggesting a metamorphic origin. A wider range of d 13 C CO2 values (from À9.94& to 20&) was associated with the mixing of microbial carbon dioxide, isotopic fractionation during CO 2 migration through the microporous structures of coals, and/or carbon isotope fractionation during gas-water exchange and dissolution of CO 2 . Away from the F19 fault, the volumes of micropores, mesopores and macropores decrease gradually. The Dubinin-Radushkevich (DR) micropore volume decreased from 0.0059 to 0.0037 cm 3 g -1 , and the mesopore and macropore volumes decreased from 0.066 to 0.026 cm 3 g -1 . The CO 2 injection can mobilize aromatic hydrocarbons and mineral matter from coal matrix, resulting in the decrease in the absorption peak intensity for coal samples after supercritical CO 2 treatment, which indicates that chemical reactions occur between coal and CO 2 , not only physical adsorption.

ABSTRACT:The spherical Voronoi diagram is a type of the global data model in Digital Earth which has become increasingly important and a lot of efforts have been done to develop the algorithms. However, most of the prior works were in vector mode and based on point sets. Recently, some approximation raster-based algorithms were presented which can generate spherical Voronoi diagrams for point, curve, and face sets easily. However, almost all these raster-based algorithms are based on dilation operation and the dilation errors increase greatly with the growth of dilation steps. To overcome this deficiency, a novel GSG-based algorithm for generating spherical Voronoi diagram is proposed in this paper. In our algorithm, distance computation and comparison based on GPU are used instead of dilation operation to diminish the Voronoi error and improve the efficiency. Results show that line sets and area sets can be handled as well as point sets in this algorithm and the Voronoi error can be limited within half of one grid. Additionally, the efficiency for generating spherical Voronoi diagram is improved greatly.

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