Assessment of Kinetic Characteristics for Coalbed Gas from Thermodynamic Measurements in Sealed Canister with Coal Chippings

The authors theoretically substantiated and, using in-situ measurements, proved the method of determining kinetic characteristics for coal bed gas: content, diffusion factor, mass exchange and rate of desorption. These data are required for the development of technologies of coal mining and methane utilization. The method involves solution of an inverse problem within the framework of a nonlinear model of gas emission from a particle placed in an isolated container, using the data on time change in thermodynamic parameters (pressure and temperature) in a sealed canister with coal chippings. The model analysis shows that ratio of methane concentrations at different moments of time is independent of gas content. This enables development and numerical implementation of a two stage algorithm: first, by solving an inverse problem with time-dependent coefficients, the factors of diffusion, mass exchange and desorption are found; then, with minimization of a special function, the gas content is determined. The in-situ data are obtained using coal chippings from drilling in an operating mine in Kuzbass, by means of measurement of pressure and temperature in five canisters for 10 days. The interpretation of the data made it possible to assess the methane content in the test coalbed site as 4 kg/m3.