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Shen J.,Key Laboratory of CBM Resources and Dynamic Accumulation Process | Shen J.,Key Laboratory of Coal based CO2 Capture and Geological Storage Jiangsu Province | Shen J.,China University of Mining and Technology | Qin Y.,Key Laboratory of CBM Resources and Dynamic Accumulation Process | And 7 more authors.
Arabian Journal of Geosciences | Year: 2015

To investigate the sorption and diffusion behavior of deep coals, high-pressure sorption experiments of methane on coals were performed by the volumetric method. The experimental sorption isotherms fit the Langmuir model over the experimental pressure and temperature ranges. The sorption volumes of all coals tested exhibit a typical temperature behavior with a negative exponent decreasing as temperature increases. An approximately linear correlation for the methane Langmuir volume with coal rank was observed. The effect of coal rank on adsorption volume decreases with increasing temperature. The Langmuir pressure decreases initially with coal rank, reaches a minimum pressure corresponding to the maximum vitrinite reflectance at ∼2.2 % and then increases. Studies on the diffusion of methane in coal using a unipore diffusion model showed that the effective diffusion coefficients for the seven coals studied varied from 2.98 to 68.3 × 10−5 s−1. The effective diffusion coefficients of coal at the first pressure step generally increased linearly with increasing temperature, and a complex nonlinear relationship for methane sorption rate with coal rank was observed. Finally, an empirical equation was developed to estimate the sorption capacity of methane on coal of a given rank as a function of the coal burial depth in a time-invariant pressure and temperature field. The sorption capacity of the moisture-equilibrated coal was found to increase with burial depth until it reaches a maximum of 24 cm3/g at ∼1,500 m, followed by a slow decline to 20.5 cm3/g at approximately 3,000 m. © 2014, Saudi Society for Geosciences.

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