Abstract
Gas adsorption occurs when the dynamic adsorption equilibrium conditions of the local adsorptive sites are broken. In the overall process of unconventional natural gas generation, enrichment, storage, and production, this phenomenon plays a significant role. A double-distribution Lattice Boltzmann model for solving the coupled generalized Navier-Stokes equation and advection-diffusion equation with respect to the gas-solid dynamic adsorption process is proposed for multicomponent gas migration in the unconventional reservoir. The effective diffusion coefficient is introduced to the model of gas transport in the porous media. The Langmuir adsorption rate equation is employed to control the adsorption kinetic process of gas-solid adsorption/desorption. The model is validated in two steps through fluid flow without and with gas diffusion-adsorption between two parallel plates filled with porous media, respectively. Simulation results indicate that with other parameters being equal, the rate of gas diffusion in the porous material and the area of the dynamic adsorption equilibrium-associated region increase with the matrix porosity/permeability. Similar results will happen with a greater saturation adsorption amount or a lower Langmuir pressure. The geometric effect on adsorption is also studied, and it is found that a higher specific surface area or free flow region can enhance the gas transport and the rate of adsorption.
Highlights
Coalbed methane (CBM) is one of the most important and potential energies which has been recognized as an alternative to oil and has achieved more and more attention in recent years [1]
The gas molecules of coalbed methane migrate with the fluid in the free flow region, a part of the free gas molecules will be trapped by the solid wall when they reached the interface of the free flow region and the porous medium, and more molecules enter the nanopore network and are adsorbed on the inner surface of pores
We proposed a coupled generalized NavierStokes equation and the advection-diffusion equation for gas migration in porous media which includes gas-solid adsorption and desorption
Summary
Coalbed methane (CBM) is one of the most important and potential energies which has been recognized as an alternative to oil and has achieved more and more attention in recent years [1]. More and more researchers concentrated on developing an LB model for multiple transport mechanisms with chemical reaction in the porous media He et al [19] proposed an LB model for fluid diffusion-convection with a chemical kinetic reaction using the double distribution function for controlling the fluid flow and diffusion, which introduced a source/sink term in the diffusion equation to govern the reaction process. We developed a double-distribution Lattice Boltzmann model to solve a coupled generalized Navier-Stokes equation, and the advection-diffusion equation is proposed for unconventional natural gas migration in the reservoir that includes gas-solid adsorption and desorption, which is based on the REV model of Guo and Zhao [9] and the diffusion-reaction model of He et al [19].
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