Pressure And Temperature Evolution Of Hydrate Reservoir During Production By Depressurization In Shenhu Area

Natural gas hydrate is regarded as the most promising resource in the 21st century because of its low pollution,large reserves and high energy density.The depressurization method is an effective method for the exploitation of hydrate reservoirs,so it is necessary to study the depressurization process of hydrate reservoirs more thoroughly and carefully.In the process of depressurization exploitation of hydrate reservoir,it is necessary to control the reservoir pressure to be lower than the equilibrium pressure of hydrate phase,so that hydrate can be decomposed and produced.Therefore,the propagation of pressure directly affects the decomposition of hydrate in hydrate reservoir.In addition to pressure changes,hydrate decomposition is an endothermic process,and the transfer of formation heat directly affects the decomposition rate and process of hydrate,which is directly reflected in the temperature change of hydrate reservoir.Therefore,it is necessary to analyze the law of pressure propagation and temperature change in reservoir during the process of hydrate depressurization.Firstly,the relationship between pressure front position and time,temperature front position and time,and hydrate saturation front position and time are deduced by analytic model.Then,from the point of view of numerical simulation,the mathematical model of depressurization exploitation of hydrate reservoir is established,and the accuracy and feasibility of the model are determined by fitting the actual exploitation situation of hydrate in Shenhu sea area.On this basis,one-dimensional model and three-dimensional model are established to study the movement law of pressure front and temperature front,and the influence of geological factors and development factors on the movement law of pressure front and temperature front is analyzed.The relationship between the position of pressure front and time is deduced by establishing an analytical model.The equation is as follows:(?)The relationship between temperature leading edge position and time is as follows:(?)The relationship between the position of hydrate saturation front and time is as follows:(?)The relationship between pressure front position and time obtained by one-dimensional model simulation is as follows:(?)The relationship between temperature leading edge position and time is as follows:(?)The relationship between the position of hydrate saturation front and time is as follows:(?)The relationship between pressure front position and time obtained by three-dimensional model simulation is as follows:(?)The relationship between temperature leading edge position and time is as follows:(?)The relationship between the position of hydrate saturation front and time is as follows:(?)The relationship between leading edge position and time deduced by theory can better fit the results of numerical simulation model.The increase of permeability,formation porosity,initial temperature,pressure reduction range and pressure reduction speed will accelerate the pressure front movement speed in formation,while the increase of initial pressure and hydrate saturation will slow down the pressure front movement speed.The increase of formation porosity,initial temperature,thermal conductivity,specific heat capacity,pressure reduction amplitude and pressure reduction speed will accelerate the movement speed of temperature front,while the increase of initial hydrate saturation will slow down the movement speed of temperature front.