Numerical Simulation Of Depressurization And Injection Heat Combination Method Of Natural Gas Hydrate

Natural gas hydrate with the characteristics of the abundant reserves,the high calorific value and the tiny pollution is an important strategic resource in the future,whose mining and utilization is the current research hotspot.For the moment,the most promising and potential methods of the utilizing natural gas hydrate exploitation are depressurization method,injection heat method and their combination method.At the same time,many scholars at home and abroad have focused on single depressurization method,single injection heat method,depressurization-injection-heatmethodandinjection-heat-depressurization method etc,but the combination method of simultaneous depressurization and injection heat is less,so the exploitation process of hydrate combination method is deeply studied in this paper in order to help the actual mining.The exploitation of hydrate is mainly studied by experimental simulation and numerical simulation.In terms of experimental aspects,scholars mainly explore the effect of reservoir factors,depressurization factors and injection heat factors on the hydrate exploitation process.In terms of simulation aspects,scholars simulate the hydrate decomposition mainly through the establishment of mathematical model including conservation equations,reaction kinetics equations etc.Based on the previous combination method experiment,this paper establishes a three dimensional mathematical model of hydrate depressurization and injection heat combination mining method through the computational fluid dynamics software.This model includes quality,momentum and energy conservation equations,reaction dynamic equations,permeability equations and parameter equations etc,and combines with the loading calculation expressions to explore the effect of the reservoir factors,depressurization and injection heat factors on the hydrate production process,analyzing the pressure and hydrate,gas,water three-phase change.Through simulating the hydrate combining exploitation method under different reservoir factors,it is found that when the larger the reservoir initial permeability is,the lower the reservoir pressure level is,which is conducive to control the production well pressure,so it should take measures to improve the permeability of hydrate deposits in actual exploitation.The larger the permeability decreasing index is,the greater the experience coefficient of water relative permeability n_w value is,the higher the reservoir pressure level is,which is not helpful to control the production well pressure,so it should consider the existing state of gas hydrate in actual production.The larger the hydrate initial saturation is,the longer the reaction time is,so it should choose a higher hydrate initial saturation to achieve the long-term exploitation.Through simulating the hydrate combining exploitation method under different depressurization and injection heat factors,it is found that the greater the depressurization range is,the faster the pressure propagation velocity is,the lower the reservoir pressure level is,which is beneficial to control the production well pressure,so the proper pressure reduction range should be selected in actual production.The higher the heat fluid injection rate is,the higher the heat fluid injection temperature is,the higher the hydrate decomposition rate is,the shorter the reaction time is,which is helpful to rapidly product gas,so the proper heat fluid injection rate and temperature should be chosen in actual exploitation.