A multiscale approach for simulation of shale gas transport in organic nanopores

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Gas flow behaviors in shale are significantly complicated because of the inherent complexity and heterogeneity of shale formations. Revealing the gas transport characteristic is critical for achieving high efficiency of shale gas exploitation. In this work, a multiscale approach combined molecular simulation and lattice Boltzmann method has been proposed for investigating gas transport in shale organic nanopores. Firstly, the characteristic of adsorbed gas in shale nanopore was obtained by molecular simulation. Then, the adsorption properties were integrated to develop a lattice Boltzmann model, which can capture slippage and surface diffusion effects in shale nanopores. By employing this proposed multiscale model, the effects of pressure, temperature and pore size on shale gas adsorption and transport characteristics in organic nanopore were studied. Numerical results show pore size and pressure have great influences on gas adsorption behaviors. The gas apparent permeability tends to increase with the increment of temperature and decrease of pressure. Moreover, the influences of pore size and pressure on surface diffusion permeability were examined. Numerical results indicate the contribution of surface diffusion to overall apparent permeability tends to be enhanced in small pore and low pressure. However, this influence will be greatly weakened with the increasing pore size.