Simulation Study Of Production Of Argillaceous Siltstone Hydrate Reservoir By Depressurization And Heat Injection

With the increasing demand for energy in the world,natural gas hydrate,as a clean energy with high reserves and high carbon content,has become a hot research object.Many countries have carried out research and test exploration of hydrate deposits,and China has also conducted two test explorations in the South China Sea and made good progress.Both the single depressurization method and the heat injection method have their own limitations in the development methods of hydrate reservoir,and the combined heat injection and depressurization method can make up for their shortcomings.The hydrate reservoirs in South China Sea are argillaceous siltstone reservoirs with low permeability,which are difficult to be exploited.In order to explore the feasibility of combined exploitation of heat injection and depressurization in argillaceous siltstone hydrate reservoirs and the effect of hydrate decomposition under this method.In this study,a one-dimensional permeability measurement experiment of gas hydrate cores was designed to measure the permeability variation rule during the hydrate decomposition process in cores of different components.Based on the coupling relationship of three physical fields of seepage,heat transfer and hydrate phase transformation,a mathematical model was established by introducing fluid property change model to explore the law and characteristics of hydrate decomposition in porous media by combined heat injection and pressure reduction method.Then,the heat injection time and the relative position of the double horizontal Wells were optimized by simulating the process of heat injection and depressor combined exploitation of argillaceous siltstone hydrate reservoir.As results,the permeability of porous media increases with the decrease of hydrate saturation,and the permeability increases faster with the smaller particle size of porous media.When the hydrate in argillaceous siltstone is completely decomposed,the permeability of the core decreases compared with that without hydrate test due to the influence of argillaceous hydration.At the initial stage of hydrate decomposition in porous media under the combined method of thermal injection and depressurization,there are thermal injection decomposition fronts and depressurization fronts respectively,and the depressurization is more active.After the contact of the two,the combined action of heat injection and depressurization begins to take place in the porous medium,and the residual hydrate rapidly decomposes.The center of the porous medium advances to the edge before decomposition.Reducing the outlet pressure and increasing the injection temperature are beneficial to accelerate the decomposition of hydrate,increase the gas production rate,and accelerate the temperature and pressure change process.However,the outlet pressure mainly affects the contact velocity of the decomposition front,while the injection temperature has an effect on the progress of the whole decomposition process.The decompression method should be adopted first when the combined method of double horizontal well heat injection and depressor is used to produce argillaceous siltstone hydrate reservoir.Heat injection can be started when the depressurization front is in contact with the heat injection well to obtain a larger recovery area.When the heat injection well is located directly below the depressurization well,the produced gas·water ratio decreases slowly,but it is difficult to obtain the maximum production range due to the restriction of upper and lower boundary of the reservoir.When the heat injection well is located below the depressurization well oblique,the exploration area of the hydrate reservoir can be affected by the heat injection is larger,which is more conducive to increase the hydrate recovery.