Decomposition Law And Heat Transfer Analysis Of Methane Hydrate In Porous Media By LBM Simulation

Facing the energy crisis,it is particularly important to seek clean energy.Natural gas hydrate has large reserves,high energy density and is clean and pollution-free,which is called one of the most important clean energy sources in the 21 st century.The exploitation of hydrate reservoir is a complex process involving reaction kinetics,mass transfer and heat transfer.Therefore,it is of great significance to study the decomposition mechanism of natural gas hydrate.In this paper,the Lattice Boltzmann Method(LBM)was used to first study the seepage characteristics of porous media,construct the oblique 45° square arrangement,square arrangement,equilateral triangle arrangement and diamond arrangement,and compare the simulation results with the empirical formula.Then the decomposition of gas hydrate in porous media is studied numerically.Considering the three phases of methane hydrate solid phase,methane gas phase and water liquid phase,and considering the decomposition kinetics and thermodynamics of methane hydrate in porous media,a two-dimensional model of methane hydrate decomposition in porous media was established based on lattice Boltzmann method.Big density using the lattice boltzmann method than false potential model,hydrate decomposition dynamics,solid phase surface update VOP decomposition of natural gas hydrate in porous media,the principle of simulation respectively to simulate the porosity of porous media,frame structure and the influence of the hydrate occurrence state of decomposition characteristics,and through the damm kohler(Da)characterization analysis control mechanism.The influence of heat transfer on hydrate decomposition was studied.The influence of boundary temperature change on hydrate decomposition rate was analyzed by coupling velocity distribution function with temperature distribution function.The following conclusions are drawn:(1)As the porosity of the porous media decreases,the flow in the porous media is inhibited.The porous media with rhombus arrangement has higher pore utilization rate.By comparing the simulated permeability value in this paper with the empirical formula,it can be found that the average absolute error between the simulated permeability value and the empirical formula of Lee&Yang,Ergun and Sangani when the porous media particles are arranged in an oblique45° square is 23.7%,24.4% and 38.9%,respectively.In square arrangement,they were 42.9%,44.7% and 56.5%,respectively.The mean absolute errors of the arrangement of equilateral triangles compared with Lee&Yang's and Ergun's empirical formulas are 27.7% and 22.1%,respectively.Rhombus arrangement was 62.9% and 77.4%,respectively.The equilateral triangle arrangement is the best.(2)When the influence of heat transfer of hydrate decomposition is not considered,the decomposition process of hydrate is divided into three stages: mass transfer diffusion stage,mass transfer and chemical reaction equivalent stage,and reaction control stage.The porous media with higher porosity is more conducive to the decomposition of hydrate.The hydrate in the encapsulated state decomposes more easily than that in the suspended state.When the porosity of porous media is less than 50%,the decomposing efficiency is low only by decomposing with pressure reduction and heat injection.(3)The effect of heat transfer on decomposition was considered by coupling velocity field with temperature field.Compared with the constant temperature simulation,the gas hydrate decomposition rate increases with the increase of boundary temperature,and the effect of the increase of gas hydrate decomposition rate is more obvious for the porous media with small porosity.When the porosity of the porous medium is 37.98% and the heating temperature of the upper and lower walls is 0.065(300.24K),the decomposition time is shortened by 46.9%,and when the heating temperature is increased from 0.065 to 0.1(461.91K),the decomposition time is shortened by 10.6%.