Study On Decomposition And Flow Characteristics Of Gas Hydrate Reservoir Based On LBM

Natural gas hydrate is a kind of ice-like crystal material formed by natural gas and water,which is mainly stored in deep sea floor and permafrost.Because of its high combustion heat and rich reserves,natural gas hydrate has been widely concerned by researchers all over the world.The exploitation of natural gas hydrate involves heat transfer,mass transfer and multiphase flow,and the process is extremely complex.By studying the decomposition of natural gas hydrate and the flow characteristics of fluid in porous media,the sensitivity analysis of the factors affecting the decomposition rate of natural gas hydrate is carried out,which provides theoretical and data support for the field exploitation of natural gas hydrate.In this paper,the physical model of natural gas hydrate decomposition is established,and the multicomponent multiphase flow model in lattice Boltzmann method(Lattice Boltzmann Method,LBM)is adopted,combined with the boundary condition of solid-liquid interface reaction.VOP solid renewal method and decomposition kinetics of natural gas hydrate were used to systematically simulate the decomposition process of natural gas hydrate.At thesame time,the flow characteristics of porous media containing natural gas hydrate in different states are simulated by single phase flow LBM model,and the effects of porosity,bottom hole pressure and reservoir temperature on the decomposition rate of natural gas hydrate in porous media are discussed respectively.In this paper,the following conclusions are drawn from the simulation study:(1)Based on LBM combined with hydrate decomposition kinetics,coupled gas-liquid two-phase flow,boundary reaction and solid decomposition of natural gas hydrate,the decomposition process of natural gas hydrate under pressure reduction was simulated.It is found that the depressor decomposition of hydrate is a solid phase structure evolution process,which includes mass transfer and two-phase flow,and the solid decomposition has a great influence on the reaction rate.(2)The effects of porous media with different pore shapes,hydrate with different shapes and different occurrence states on relative permeability are simulated.It is found that the circulation channel has the greatest influence on the relative permeability,and the larger the circulation channel is,the smaller the relative permeability increases with the increase of hydrate saturation.The width of the inlet of the flow field and the shape of hydrate also have different degrees of influence on the relative permeability.(3)The decomposition of natural gas hydrate under different operating conditions was simulated.The simulation results show that the higher the porosity is,the faster the hydrate decomposition rate is,the higher the reservoir temperature is,the faster the decomposition rate is,and the pressure drop has little effect on the decomposition rate of a single hydrate.In order to better exploit natural gas hydrate,the reservoir temperature should be increased properly,which will increase the decomposition rate of hydrate and accelerate the exploitation.