Study On Fracture Quantitative Characterization,Modeling And Propagation Law Of Hydraulic Fracturing In Heterogeneous Tight Reservoir

With the deepening of hydraulic fracturing research,the fracture propagation law of hydraulic fracturing under the influence of heterogeneous characteristics of tight reservoir has attracted more and more attention.Under the influence of reservoir heterogeneity,the of hydraulic fracture propagation is often random.A comprehensive quantitative evaluation system is established to accurately describe the dynamic evolution characteristics of reservoir hydraulic fracturing fractures and their field variables(stress field and displacement field),which plays an important role in revealing the propagation mechanism of hydraulic fracturing fractures under the influence of reservoir heterogeneity.Using the methods of laboratory test,theoretical analysis and numerical simulation,this paper systematically studies the quantitative characterization of hydraulic fracturing fractures from a single heterogeneous tight reservoir rock(only containing natural bedding,multi mineral components,or different heterogeneous structures)to a heterogeneous tight reservoir(containing both natural fracture network and multi mineral components)modeling and extension law.The fracture modeling and quantitative evaluation method of hydraulic fracturing in heterogeneous tight reservoir are optimized,and the fracture propagation law of hydraulic fracturing in heterogeneous tight reservoir is discussed,which plays a guiding role in the research and construction of hydraulic fracturing in heterogeneous tight reservoir.The main research results are as follows:(1)The test results show that the heterogeneity characteristics of different types of rock samples are different,and the multi mineral components and natural fractures in coal and rock are the most complex.The natural fracture length basically conforms to the power law distribution,and the power index is 1.522.Hydraulic fracture propagation is easily affected by fluid injection rate and minimum in-situ stress,and the heterogeneity of different rock samples in the same reservoir area may be the inducement of the discreteness of hydraulic fracture propagation.(2)Based on the finite element discrete element method(FDEM)and twodimensional digital core reconstruction technology,a new hydraulic fracture inversion simulation method is proposed.Its reliability is verified by comparison with the experimental data.Factor analysis shows that this method can overcome the problems of mesh generation and convergence in fracture evolution simulation,and the reconstruction accuracy can be improved with the improvement of resolution.This method provides a method support for the subsequent hydraulic fracturing simulation modeling.(3)The existing quantitative characterization methods are improved.Based on the principle of vector statistics,a new quantitative characterization and reconstruction method of rough fractures is proposed.The test results show that the improved cube covering method is more conducive to obtain stable fractal dimension.The new quantitative characterization and reconstruction method of rough fractures has significant advantages in the quantitative characterization and reconstruction of rough fractures.The difference of quantitative parameters before and after reconstruction is less than 5%,and the obtained discrete fracture network model is conducive to the generation of high-quality mesh.This method provides a method support for the subsequent discrete fracture network modeling and quantitative characterization of hydraulic fractures.(4)The hydraulic fracture propagation under the influence of different heterogeneous characteristics is studied.The results show that when affected by natural fractures,coal hydraulic fracturing is easier to form complex fractures than shale hydraulic fracturing.When affected by different control mechanisms,the hydraulic fracture propagation under the toughness control mechanism is more vulnerable to the rock elastic modulus,element size and far-field in-situ stress of Weibull distribution than that under the viscosity control mechanism.Under the influence of multi mineral components and natural fracture distribution in rock,hydraulic fractures are prone to asymmetric propagation,bending propagation and macro steering.(5)The hydraulic fracture propagation under the comprehensive influence of rock elastic modulus of different discrete fracture networks and Weibull distribution is compared and studied.The results show that the fracture path in the relatively homogeneous model based on conventional and rough discrete fracture network has an important influence on the evolution of hydraulic fracturing fracture parameters such as length,aperture,area,tortuosity and different fractal dimensions.When there are natural fractures,the influence of conventional and rough discrete fracture network on hydraulic fracture propagation is also significantly different.When further considering the distribution of rock elastic modulus,the hydraulic fracture propagation appears to be discrete.