LBM Simulation Of Multiphase Flow In Porous Media Containing Natural Gas Hydrate

As one of the most important clean energy in the new century,natural gas hydrate is widely concerned and studied all over the world due to its high calorific value and abundant reserves.Natural gas hydrates in nature are mainly in the permafrost zone deposits or seabed sediments,and the storage of geological conditions is complex.The rational and safe exploitation of the gas has become a hot spot for many researchers.The exploitation of hydrate reservoir is a complex process involving heat transfer,mass transfer and kinetic reaction.There are many factors affecting the gas,liquid and solid phase flow in hydrate deposits,which directly affect the mode of heat and mass transfer and efficiency.It is also the basis of selecting hydrate mining scheme and determining the efficiency of mining.Therefore,the study of multi-phase flow mechanism of natural gas hydrate in sedimentary layer is of great practical significance for the exploitation of natural gas hydrate.Based on the mesoscopic method,a two-dimensional porous medium is reconstructed by four parameter growth method in MATLAB,and hydrate is added to the porous medium.The D2Q9 model and Shan-Chen model in the lattice Boltzmann method are used to simulate the methane gas single phase flow and the gas-liquid two-phase flow respectively,and the methane in the porous medium is studied.Single phase flow,single phase flow of hydrates,methane and water two phase flow and gas-liquid two phase flow of hydratescan be obtained,and the variation of relative permeability of gas and liquid can be obtained.The conclusions are as follows:(1)when the porosity of porous medium increases gradually,the permeability of methane gas increases as the porosity of porous medium increases,which indicates that the connectivity of porous media has a certain influence on the flow of methane gas.And the larger the porosity,the better the circulation.Based on this conclusion,we can improve the production of gas hydrate by improving the porosity of the stratigraphic sediments,such as increasing the porosity of the sediments by hole injection.(2)when the gas hydrate is single phase flow,different natural gas hydrate saturation is set,and the methane gas permeability is calculated to change the variation curve of the methane relative permeability with the hydrate saturation.It can be found that the relative permeability of methane decreases exponentially with the increase of methane saturation when the porosity of porous media is constant,and the effect of hydrate on the relative permeability of methane is greater.The reason is that the hydrate formation in the center of the pore makes the flow channel become relatively narrow,the flow velocity of methane gas decreases,and the phase permeability is reduced,thus the absolute permeability of methane is changed.And the porosity of porous medium does not affect the curve of the relative permeability of methane with the change of hydrate saturation.The reason is that the porosity increases or decreases,and the absolute permeability of methane is increased and decreased with the addition of hydrates and non hydrates,and the degree of change is close,so the ratio of the relative permeability of methane almost does not occur.Therefore,the change of porosity does not affect the migration of methane relative permeability curve.(3)when gas-liquid two phase flow occurs in hydrates,pores are occupied by hydrates,methane and water.As the saturation of hydrate is constant,the relative permeability of gas and liquid can change with the methane saturationby changing the methane saturation.At the same time,the effect of hydrate saturation on the relative permeability of gas and liquid can be obtained by changing the saturation of hydrate.When the methane saturation is low,the relative permeability of water is almost constant.With the increase of methane saturation,the relative permeability of water decreases faster and the relative permeability of methane is increasing.It can also be obtained that the gas and liquid relative permeability curve will be offset by changing the saturation of hydrate,the higher the hydrate saturation,the greater the migration of gas and liquid relative permeability curve.The reason is that when the methane saturation is constant,the increase of hydrate saturation makes the flow channel become more narrow and complex,the flow velocity of gas and liquid is relatively reduced,the influence of hydrate saturation and gas-liquid two phase flow on the phase permeability is superimposed,which makes the variation range of the gas and liquid phase permeability higher than the absolute permeability value of the single phase flow.The ratio of the relative permeability of gas and liquid will be reduced,and the relative permeability of gas and liquid is shifted with the variation of methane saturation,and the greater the saturation of hydrate is,the greater the offset degree.