Study On Numerical Modeling Of Heterogeneous Rock Material And Hydrualic Fracture Propagation Based On Homogenization Method

As a favora technology to extract oil and gas resources,hydraulic fracturing has been studied by numerous scholars.Compared with theorical method and experimental study,numerical simulation shows the characteristics of low cost and high benefit.Meso-structural chasteristics of heterogeneous rock materials can not only reflect its failure mechanism,but affect macroscopic mechanical properties as well.Therefore,this paper focuses on the modeling method of heterogeneous rock materials,and then characteristics of hydraulic fracture propagation is studied among meso-scale based on existing model calculating hydraulic fracture.Natural rocks have complex-meso-structurial characteristics under long-term geological action,and boundary shapes of rock mentioned above can be described by simplified geometries such as circle,ellipse and polygon.First of all,a level set function is established by incroducing Perlin Noise to elaborate boundars of irregular particles based on ones describing regular particles,and algorithm detecting the relationship between particles is given.The heterogeneous rock model filled irregular particles without overlap between particles is established in two-dimension region.In addition,although it can realize the distribution of particle shap independent from finite element grid that the level set method is used to describe material boundary,it cannot consider meso-characteristics of particle boundary.Based on the method above,effective material parameters of Gauss integral point in the elements accrossed boundary of materials will be calculated once more using homogenization method.By compared with theorical solution,LSF-MT has the capacity of considering boundary characteristics of meso structure in modeling of heterogeneous rock.Last but no least,the model,combined with the heterogeneous rock model established by LSF-MT and hydraulic fracture model established by PHF,can be used to simulate hydraulic fracture propagation of heterogeneous rock considering meso boundary features,and effective factors about geometric characteristics of hydraulic fracture and breakdown pressure from heterogeneous rock are analysed.The results from paper indicate that LSF-MT method can effectively consider irregular particle boundary characteristics.By studying further application range of LSF-MT method in terms of the type and spactial location of filled particles,there are the larger error compared with theoretical value,the larger volume fraction of particles.The error is similar between LSF-MT and LSM when the numerical model is filled with single particle.Nevertheless,when numerical model contains numerous particles,it is essential to consider the material boundary characteristics using LSF-MT method.Sensitivity index represented geometric feature of crack indicates that injection water has enormous influence in homogeneous rock model generated by PHF,while permeability of rock has little influence.Meanwhile,simulation solution from hydraulic fracture model to heterogeneous rock established by PHF-LSF-MT method states that breakdown pressure approaches theoretical value when distribution features of rocky boundary are considered.