Study On Inverse Problem From Surface Displacement Monitoring To Solving Fluid Injection Into Reservoir

The process of injecting natural gas into an underground gas storage or water injection fracturing and other fluid injection into the reservoir will cause disturbance of the original stress field and displacement field,and the uplift or subsidence of surface will also be induced.Obtaining deep dynamic information in the process of reservoir stimulation through inversion of far-field displacement monitoring data is helpful to monitor the operation status of gas storage or guide the exploitation of unconventional oil and gas resources.However,there are few researches on reservoir inverse problems,and most of them focus on inversion to solve the strain or parameters such as elastic modulus of the reservoir.Based on the Displacement Discontinuity Method and the Spatial Regularization Method,an inverse problem solving method for elastic problems is proposed in this paper.The source program is compiled to calculate the load on the fracture during hydraulic fracturing.The specific contents and conclusions of this article are as follows:(1)First,the of Boundary Element Method and Inverse Problem is reviewed.The status of Boundary Element Method applying in Inverse Problem solving,the engineering practice of Inverse Problem,and reservoir monitoring methods are reviewed.Through literature research,it can be found that there are few studies using the far field monitoring displacement of the reservoir to solve the deep reservoir load.Therefore,this paper studies the pressure inversion of the reservoir.(2)The numerical simulation method of the Boundary Element Method Is Described,in which the Displacement Discontinuity Method introduced in detail.In addition,the theoretical basis of Inverse Problem solving is also discussed.It laid a foundation for the subsequent combination of regularized equation solving method and Boundary Element Numerical implementation to solve Inverse Problem.(3)A simplified modeling analysis of the inversion of surface deformation caused by reservoir injection fluid is carried out in this chapter.Two-dimensional elastic Inverse Problem is defined and a program using Boundary Element Method is compiled.An example of a square thin plate with a circular hole is used for verification.The results show that even when the number of sensors is small and there are errors in the monitoring data,a accurate boundary load result can be obtained.Then,the inverison of the pressure at the fracture in a shallow coal seam in Alberta is analyzed in two dimensions.As a result,it is found that the inverse result obtained in the middle of the fracture is ideal.In order to analyze the reason for result in at both ends of the fracture,the inverse analysis of the pressure from the round hole to the ellipse hole under the surface was carried out.Comparing the accuracy of the results under different curvatures,it can be concluded that the change in curvature is related to the error of the accuracy of results.(4)A preliminary exploration of the inverse problem of three-dimensional elasticity is carried out.The Spatial Regularization theory in two-dimensional conditions is extended to three-dimensional,and the boundary element expression is obtained.Based on this,the three-dimensional inverse solution source program is compiled.Analysis of the disc crack example: First,the forward simulation result is compared with the analytical solution,and then the forward simulation calculation is used to obtain the displacement of the monitoring point for inverse calculation analysis.The result proves that the Spatial Regularization is in the three-dimensional inverse problem Effectiveness.A preliminary exploration of the Inverse Problem of three-dimensional elasticity was carried out.The Spatial Regularization theory in the two-dimensional case is extended to three-dimensional,and the equation expressed by Boundary Element Method is obtained.On this basis,a three-dimensional inverse calculation source program was compiled.The epenny-shaped crack is studied as an example.The results prove the effectiveness of Spatial Regularization in 3D inverse problemsThis paper provides a new idea for the analysis of monitoring data and a reference way for analyzing reservoir information.