Study On The Characteristics Of Gas-liquid Two-phase Flow In Porous Media Based On LBM

The seepage process in porous media widely exists in the fields of petroleum and natural gas extraction,CO₂ geological storage,micro-electromechanical systems,etc.,and it has recently received more and more attention.Micro-nano-scale pores are the main channels for fluid percolation in porous media.Unlike conventional-scale flow,gas flow in micro-channels has a micro-scale effect,which will cause changes in percolation properties.In this paper,based on the MRT-LB model,considering the influence of the Knudsen layer on the gas flow,combined with the high density ratio multi-component multi-phase pseudo-potential model,a micro-scale multi-component multi-phase LB model is constructed,and the model is used to study gas seepage in micro-channel and the influence of geometric properties of porous media,wettability and micro-scale effects in the two-phase seepage of methane gas and water.When applying this model to simulate gas flow in microchannels,it is found that the micro-scale effect will increase the apparent permeability of the gas,and with the increase of the average Knudsen number of the pores,the velocity difference between the velocity near the pore wall and the center of the section Decrease.Analyzing the distribution of high permeability regions in porous media under different average Knudsen numbers,it is found that as the average Knudsen number increases,the proportion of the area of high permeability regions in the pores to the total pore area increases,and the high permeability regions preferentially increase from small pores.which is due to the larger proportion of the small pores relative to the large pore Knudsen layer.When applying this model to study the characteristics of methane gas and water two-phase seepage flow,it is found that the flow of methane gas and water two-phase fluid in porous media is affected by the shape of porous media particles,specific surface area,homogeneity,wettability,and micro-scale effects.Specifically,the porous medium of round particles has lower flow resistance than square particles,and the relative permeability of both the water phase and the gas phase increases.When the porosity of the porous medium remains unchanged,the larger the specific surface area of the solid particles,the larger the contact area between the fluid and the solid,which is not conducive to seepage,but on the other hand,larger specific surface area is beneficial to the formation of continuous seepage zone,which is beneficial to the seepage of water phase.This effect is more obvious when the saturation is small（S_w<0.4）,so the relative permeability of the water phase first increases and then decreases.Compared with homogeneous porous media,heterogeneous porous media has larger pore tortuosity,which is unfavorable to the seepage of both the two phases,so the relative permeability of the two phases is reduced.In porous media,the wetting phase tends to occupy a smaller pore space while the non-wetting phase tends to occupy a larger space.This mechanism makes the permeability of the non-wetting phase increase and that of wetting phase decrease with the increase of wall wettability.On the other hand,in strong wetting medium,water phase is easier to form a continuous seepage zone,which is conducive to the seepage of water phase.Therefore,the relative permeability of water phase decreases first and then increases.The micro-scale effect will cause the gas to have a slip velocity.This effect increases the permeability of the non-wetting phase and the wetting phase,but the increase of gas velocity is not conducive to the continuity of wetted phase when liquid saturation is low,which will inhibit the seepage of the wetting phase.These two mechanisms work together to increase the relative permeability of the non-wetting phase,while the relative permeability of the wetting phase does not change significantly when increasing the average Knudsen number of the pores so that the flow enters the slip zone from the continuous flow zone.