基于格子Boltzmann方法的超临界甲烷多层吸附模拟OA

Adsorbed gas represents a unique occurrence state of methane in shale gas reservoirs,distinct from conventional gas.Its adsorption behaviors significantly impact the reserves assessment and production performance numerical simulation of shale gas reservoirs.The current studies on adsorbed gas using the lattice Boltzmann method(LBM)are mostly based on the monomolecule layer(or monolayer)adsorption model,which is inconsistent with findings from that reveal evident multimolecule layer(or multilayer)adsorption of shale gas in micro-and nano-pores.This discrepancy leads to an incomplete understanding of gas occurrence and transport mechanisms.To address this issue,a Lattice Boltzmann model that incorporates supercritical multilayer gas adsorption was constructed to investigate the multilayer adsorption mechanisms of supercritical methane in micro-and nano-pores on gas mass transfer.The following results are obtained.First,compared to monolayer adsorption,multilayer adsorption can more accurately represent shale gas occurrence.Second,the surface diffusion velocity of gas in the adsorption layers decreases with increasing pressure and increases with rising temperature,exhibiting a typical thermodynamic sensitivity.Third,the increase in adsorption distance weakens the confinement of pore walls on methane molecules,resulting in higher flow velocity in the second adsorption layer than in the first adsorption layer.Fourth,under decreased pore diameter,multilayer adsorption significantly enhances the contribution of surface diffusion to total flux,while intensifying flow restriction and reducing matrix permeability.The conclusion is that the Lattice Boltzmann model established in this study provides a more scientific and reasonable representation of the multilayer adsorption phenomenon of supercritical methane in shale reservoirs,offering theoretical insights into fluid occurrence and mass transfer in deep,high-pressure shale gas reservoirs.