Numerical Simulation Study On The Production Of Natural Gas Hydrate Using Geothermal Energy

Gas hydrate is a kind of clean and environmentally friendly alternative energy,it is large in reserve high in energy density and is not exploited on a large scale,so that it has profound value in relieving energy crisis.Decomposition of natural gas hydrate is an endothermic process.Thermal stimulation method can provide energy for the decomposition of the hydrate,thus can greatly promote the decomposition rate of gas hydrate,obtain better development effect.However,conventional thermal stimulation method requires a lot of investment on the ground and cost a lot in thermal energy,results in poor-economy.At the same time,it can form large amount of harmful gas and consume a lot of fossil fuel in the process of forming hot fluid.In order to improve the efficiency of gas hydrate exploration and use geothermal energy as a heat source to realize cooperative exploitation of geothermal energy and gas hydrate,a method of development of gas hydrate reservoir with the utilization of horizontal heat exchange well to inject cold water as heat container is proposed in this article.A horizontal well which extends to geothermal layer is used to heat the cold water and lead the water upward to hydrate layer so as to realize the heat stimulation production method.This method uses well bore to heat the fluid and avoids hydraulic fracturing,reducing the harm to formation and declining the cost.Comparing to the conventional heat stimulation method,fossil fuel is not needed in this method to heat the fliud,so that it has the characteristic of low-carbon.In this article,the project of development of gas hydrate reservoir using geothermal method is designed,the mechanism of gas hydrate decomposition is studied.Based on the kinetic model,the formation and decomposition of gas hydrate are realized in numerical simulation,the key parameters in the reaction are determined.And then,based on the Shenhu hydrate reservoir,numerical model of geothermal production method is established,the well bore temperature of heat exchange well and the production effect during development of hydrate reservoir are studied.The results shows that,the decomposition of hydrate in the middle of reservoir is obvious by the method of using geothermal energy.Compared with the decomposition of hydrate concentrated at top and bottom of reservoir by depressurization,this method has great effect in the enhanced recovery of natural gas.Comparing with depressurization method,the reservoir parameters and development parameters which influence heat exchange effect and development effect are studied.And the influence rule of each parameter is concluded.In addition,the sensitivity of parameters are analysed.Finally,using the integrated energy conversion factor as target function,the development parameters of geothermal method are optimized by particle swarm optimization.A set of most optimized parameters is determined.Through the comparing to hot water injection method,the results can be concluded that the optimized geothermal method has economic advantage under the condition of same production effect with heat injection method.