Study On Mechanism And Numerical Simulation Method Of Multiphase Flow-geomechanical Deformation Coupling In Tight Oil Reservoirs

Tight oil is widely distributed in China and has broad prospects for exploration.It has been found in Ordos,Junggar,Songliao,Bohai Bay and Sichuan basin.The pore throat of the tight reservoir is very small,which belongs to the sub micron and nanometer grade throat,and the influence of the deformation on physical parameters of the tight oil reservoir is much higher than that of the conventional reservoir.In addition,the development of tight reservoir is characterized by natural fractures,artificial fractures,and so on,which intensifies the fluid solid coupling effect in the development of tight reservoirs.In order to reveal the deformation law of multi-media in different development stages in tight oil reservoir and study the effect of coupling of flow and deformation interaction on reservoir performances.The coupling of multiphase flow and reservoir deformation during fracturing and production was stated,based on the mechanics mechanism of multi-media deformation on tight sandstone reservoir.Through the experiment of the tight reservoir cores,we obtained the dynamic variation of matrix cores,fracture core and artificial fracture in the process of boosting and step-down process,and we also compared the difference of stress sensitivity under changing of pore pressure and changing confining pressure conditions.According to the way of coupling,the fluid solid coupling is divided into two types: pseudo coupling and fluid-solid coupling.The pseudo coupling is taken into account of the physical properties,without having to deal with stress and strain of rock.In this paper,under the pseudo coupling,the dynamic model of reservoir parameters for different development stages and the multiphase seepage mathematical model were established.On this basis,an integration of fracturing and production software module was developed.The simulation results are as follows:(I)In the fracturing process,the pore epanded and the nature fracture opened once the injection pressure was higher than the opening pressure and the artificial fracture formed once the pressure was higher than the formation fracture pressure,as a result the reservoir porosity and permeability significantly increased in fracturing process.(II)In the production process,since the decrease of pressure,the pore shrank and the fracture closed once the pressure was lower than the closing pressure,consequently the reservoir permeability decreased sharply.In the multiphase flow and geomechanical deformation coupling,the stress and strain were needed to calculate,so it need an extra rock mathematical model to describe the reservoir rock deformation,the model of seepage and deformation were solved by finite difference and finite element method.on the basis of this,the process of wells Injection-production was simulated and studied.The results The simulation results are as follows: matrix expanded and the fracture opened near Injection wells,and the matrix shrinked and the fracture closed nery production well,Thus it adversely affected the oil production.