Study On Fracturing Mechanism Of Horizontal Well In Tight Sandstone Reservoir In Songnan

China has a vast territory and is rich in unconventional oil and gas resources.With the development of conventional oil and gas resources,the reserves of conventional oil and gas resources decrease and the development difficulty increases.After the unconventional oil and gas resources are well developed,the excessive dependence of China’s oil and gas resources on foreign countries can be greatly alleviated.Tight oil and gas is one of the important unconventional oil and gas resources at present.Conventional hydraulic fracturing is difficult to achieve good economic benefits in oilfield development.Drawing on the development experience of shale oil and gas,using volume fracturing technology is the primary means to realize commercial development of tight oil reservoirs at present.The development of natural fractures,uneven distribution of strata and poor surface conditions lead to great differences in physical parameters of tight sandstone reservoirs,which have obvious heterogeneity.Like conventional fracturing design,sandstone reservoirs in the same horizontal well are generally treated as homogeneous layers,and the same cluster perforation and fracturing parameters are used.The fracturing design results are quite different from the actual fracturing effect of reservoirs,which will affect the effect of reservoir stimulation and reconstruction to some extent.However,considering the heterogeneity of different reservoir physical parameters in fracturing design,the fracturing effect is more in line with the actual fracturing effect of the reservoir.However,the mechanism of fracture propagation under the condition of considering reservoir heterogeneity is not clear,which can not guide the field fracturing design well,so it is necessary to conduct in-depth research.In this paper,based on the tight sandstone reservoir in Songnan,the fracturing mechanism of horizontal wells in heterogeneous sandstone reservoir is studied by combining rock mechanics and physical properties experiments,theoretical model establishment and verification,numerical simulation and other methods.The specific research work is as follows:(1)The rock physical properties test experiment and the X-ray diffraction experiment of core mineral components were carried out.By analyzing the experimental results,the rock mechanics parameters of sandstone reservoir are provided for subsequent simulation,and the heterogeneity of sandstone reservoir is revealed.Weibull distribution is selected to characterize reservoir heterogeneity.(2)Based on the heterogeneity of sandstone reservoirs in different degrees,the propagation law of multi-cluster hydraulic fractures is studied on the basis of strong heterogeneity of reservoirs.Based on the Weibull distribution of physical parameters of sandstone reservoir,considering the characterization of elastic modulus,a multi-cluster hydraulic fracture propagation model is established,and the influence of multi-cluster hydraulic fractures on reservoir hydraulic fracture propagation behavior under different heterogeneity degrees is studied.For strongly heterogeneous reservoirs,the effects of the difference in geostress,the tensile strength of reservoir rocks and fracturing operation parameters on the propagation behavior of multiple fractures are analyzed,and the influence law of stress interference between fractures on the propagation behavior of hydraulic fractures is revealed.The analysis and simulation results show that: in heterogeneous reservoirs,multiple clusters of hydraulic fractures show asymmetry when they expand;With the enhancement of reservoir heterogeneity,the greater the interference of stress between fractures,the more effective the suppression of fracture length,and the smaller the total fracture length;The smaller the geostress difference and tensile strength,the greater the total length of hydraulic fractures;When designing fracturing construction parameters,it should be considered to increase the cluster spacing in heterogeneous reservoirs and reduce the interference of perforation clusters and stress between fractures in order to obtain better fracturing effect.(3)In view of the random natural fractures in sandstone reservoirs,the intersection of hydraulic fractures and natural fractures is simulated by numerical simulation method with global embedded cohesion elements,which makes up for the deficiency of finite element expansion method.On the basis of strong heterogeneity,a new model of random propagation of hydraulic fractures with natural fractures is established,and the propagation law of hydraulic fractures in fractured sandstone reservoirs is studied.Using the built-in Python language of ABAQUS platform for secondary development,the global Cohesive element is given to the model grid,and the influence of hydraulic fracture random propagation in fractured sandstone reservoir is explored,and the influence of geostress difference and fracturing fluid injection displacement on the random propagation behavior of hydraulic fracture is analyzed.The analysis and simulation results show that: when the stress difference is small in strongly heterogeneous reservoirs,fracture propagation is easy to be captured by natural fractures,and along the natural fractures,a complex fracture network is formed,which improves the fracturing effect;When the stress difference is large,the expansion direction tends to the direction of the maximum horizontal principal stress,forming a relatively single hydraulic fracture,and the fracturing transformation effect is not good.