Numerical Simulation Of Fractured Tight Sandstone Gas Reservoir And Its Application

During the production of fractured tight sandstone gas reservoirs,which have strong heterogeneity and developed fractures,the permeability of matrix and fracture decrease due to formation pressure drop.Existing numerical simulation methods for such reservoirs failed to consider the nonuniformity in stress sensitivity of matrix and fractures under heterogeneous conditions.Although the embedded discrete fracture model(EDFM)has improved the computational efficiency,it is not completely applicable to fractures with low conductivity,and the near-well mesh precision is insufficient.In view of the above problems,the modeling method for fractured tight reservoirs was improved,a numerical simulation method considering non-uniform stress sensitivity was established,and a multi-scale numerical calculation method based on multiple hybrid grids was formed,which have provided theoretical guidance and technical support for developing the seepage theory of complex gas reservoirs and improving the development effect of fractured gas reservoirs.(1)The permeability characterization method based on fractal and machine learning was established respectively.Under the condition of limited data,the heterogeneous reservoir model reflecting the actual reservoir characteristics can be quickly established.Based on the porosity of the classic case SPE10,the permeability field was reconstructed by combining the fractal model.According to the characteristics of Xu2 fractured gas reservoir,the permeability prediction model constructed by fine tree algorithm was selected to be the closest to reality.(2)For structured grids,by improving the projection mode of fracture plane in Projection-based embedded discrete fracture model,expanding the stress-sensitive model based on particle deformation,a numerical simulation method was established considering the non-uniform stress sensitivity of matrix and fracture.Co MPared with the calculation results of classical exponential model,the correctness of the proposed model was verified.With the model,the correction coefficient for stress sensitivity can be obtained adaptively according to the difference of reservoir physical property.The nonuniform stress sensitive law of matrix,natural fracture and fractured fracture was revealed.(3)Layered unstructured mesh,segmented radial mesh and embedded discrete fracture coupling multi-hybrid mesh were established.A projection method for p EDFM suitable for unstructured grids was proposed to correct the conductivity of unstructured grids.Based on the multiple hybrid grid spatial domain,a multi-hybrid grid multi-scale numerical method was established with the multiscale restriction smoothed basis method,which improved the computational efficiency.The reliability of the multi-scale numerical method was verified by co MParing single-phase simulation results of the conventional finite volume method.In the calculation process for gas water two phase flow,the improper coarse grid division will result in a large error in the simulation results,and the accuracy will be seriously distorted.Thus,grid refinement of near wellbore area could improve the simulation precision and computational efficiency by using the proposed method.(4)The models proposed in this paper were applied to the Xu2 gas reservoir in the western Sichuan Basin.The non-uniform stress-sensitive plates of matrix,natural fractures and fractured fractures were established.The water invasion models considering different water energy,different stratification types and different fracture patterns were established to predict the productivity of gas wells according to production dynamic analysis,and the predicted results were consistent with the reality.In this thesis,the simulation method for stress sensitive fractured tight sandstone gas reservoirs was developed.The research results have significant theoretical meaning and application value for the determining of uneven permeability distribution in the caused by stress sensitivity in spatial and time domain,revealing the complex gas and water seepage law in water-containing fractured tight gas reservoirs,and precisely predicting the productivity of gas wells.