Numerical Simulation Of Natural Gas Hydrate Dissociation And Thermal Front Analysis By Heat Injection

The law of heat transfer between dissociation zone and hydrate zone is important to evaluate the heat conduction and energy efficiency during gas hydrate dissociation.So,the movement rule of dissociation front is necessary to study.A 3D numerical model is developed with CMG-STARS.The model involves phase equilibrium,methane hydrate dissociation kinetics,mass conservation,energy conservation,heat conduction and convection.By matching the results of experiment with the numerical model,key parameter(decay rate)is got.The feasibility of the software is verified by matching the numerical simulation results with the results of TOUGH-Fx and production test of Mallik hydrate deposit.The conclusions are: the dissociation front movement caused by depressurization moves slower than that caused by heat injection,which is mainly decided by heat convection not by heat conduction;Parameters affecting dissociation front movement are analyzed including geological parameters and development parameters;among geological parameters,the most sensitive parameters are original hydrate saturation,porosity,the less sensitive parameters are absolutely permeability and heat conductivity coefficient of rock;heat injection is not recommended for hydrate with high saturation(Sh?0.6),or hydrate with high porosity and low saturation;among the development parameters,the movement of dissociation front is mainly affected by bottom hole pressure of producer,the water temperature and the hot water injection time.With the same heat energy injected,the affection of water injection rate is weak.Depressurization method and combination of depressurization and heat injection are applied on Mallik hydrate development.For depressurization,there is obvious dissociation front at perforated layers.For the combination of depressurization and heat injection,dissociation fronts of upper layers moves slower than those of lower layers.The upper layers are fully dissociated.This is because the upper layers are of high permeability,low porosity.And also,the heat transferred from cap rock contributes to upper layer hydrate dissociation.