Research On Coupling Mechanism And Seepage Law Of Seepage And Stress Fields In The Ultra-high Water Cut Stage Oil Reservoirs

With the development of water injection in the oil fields for several decades,most of the domestic oil reservoirs have entered an ultra-high water cut stage,this makes further exploitation of the oil reservoirs more difficult.Especially after the process of high pressure water injection and circulating water injection,the reservoir pressure,stratigraphic pore structure and fluid parameters are constantly changing,which leads to irregular deformation of reservoir porous medium.At the same time,this kind of deformation will also affect the seepage effects of the formation fluid,which makes the fluid-solid coupling of ultra-high water cut reservoir more obviously.In order to understand the stratigraphic profile of oil reservoirs with ultra-high water cut stage.In this paper,a series of experiments of reservoir physical characteristics change in ultra-high water cut stage have been designed.Through rock stress-strain tests,oil-water relative permeability tests,rock pore pressure tests and oil displacing experiments,The change of rock mass structure and fluid parameters after the increase of moisture content in reservoir is compared and analyzed.Therefore,the effect of the change of moisture content on the seepage law of reservoir can be found intuitively from the perspective of physical experiments.On the basis of physical experiments,the equations of state of fluid and solid in porous medium are obtained,and combined with the effective stress principle,the energy conservation equation,the law of mass conservation,A coupled oil-water two-phase flow model was established,including the control equations of the stress field and the seepage field,and the corresponding solution conditions.And then based on the mathematical transformation and integration of the established coupling model,a fully coupled mathematical model with unknown parameters of the rock mass displacement,oil phase pressure and water saturation is obtained.According to the solution needs of different fields in the coupled model,the solution of the finite-element method is introduced and a targeted solution is adopted: The pressure is solved by the finite-element method,the saturation method is solved by the finite volume method,the displacement field is solved by the Galerkin finite element method,and the stress field is solved by the least squares method.Combining the fluid-solid coupling equations and the corresponding solution conditions.According to the established finite-element equations,a numerical simulation program was compiled with the Fortran language,and a single injection-production well group is designed to simulate the conventional water injectiondevelopment.The fluid-solid coupling model established and the corresponding finite element numerical solution in this paper,it can be used to simulate and analyze the changes of rock skeleton structure,rock stress-strain,porosity,permeability and reservoir pressure with time and space under different mining stages of the water injection reservoirs.It provides a reference for the numerical simulation of ultra-high water cut stage reservoirs and the adjustment of the later period.