Study On Hydraulic Fracture Propagation Of Chang 8 Reservoir In Pengyang Area

Due to its characteristics of low formation energy,high crude oil viscosity and nonhomogeneity,the development of the Chang 8 reservoir in the Pengyang area is not ideal,and hydraulic fracturing is an essential means to achieve increased and stable production.However,the development of natural fractures in the target block,the mechanism of mutual interference between hydraulic fractures and multiple natural fractures is still unclear,and the unclear and unsystematic theoretical understanding greatly affects the fracturing design and transformation effect.Therefore,it is important to clarify the influence of different factors on hydraulic fracture expansion in the target block for the optimization of on-site fracturing design and reservoir residual oil potential exploration.In response,this paper uses a combination of indoor experiments and numerical simulations.The rock mechanical properties tests deepened the understanding of reservoir physical properties and evaluated the reservoir compressibility.The effect of different rock mechanics parameters and fracture construction parameters on the fracture extension pattern was analysed using a large size true triaxial hydraulic fracturing system.Based on the ABAQUS software XFEM and the Cohesive unit method,the degree of influence and the influence law of the hydraulic fracture extension pattern under the directional shot fracture steering mechanism and the mutual interference mechanism of multiple natural fractures were investigated.The results indicate that the target block is less brittle,with a relatively small ground stress discrepancy factor and an average degree of natural fracture development,but the block still has the ability to form a complex fracture network,as obtained from the compressibility evaluation.The indoor experimental results show that under high horizontal ground stress difference and shot-hole completion conditions,the fracture initiation pressure is low and a good transformation effect can be obtained within 60° shot-hole azimuth.The use of variable viscosity or variable displacement fracturing makes it easier to open natural fractures to form a complex fracture network.Numerical simulations of shot steering show that with high Young’s modulus,low tensile strength,small horizontal stress difference,shot angle within 60°,larger fracture fluid displacement and viscosity,the fracture steers further and the reservoir reformation volume is larger.Numerical simulations of hydraulic and natural fracture intersections yield that hydraulic fractures usually extend in the direction of large natural fractures due to the resistance effect of small pinch angles.When a single natural fracture exists,the smaller the horizontal ground stress difference and the larger the angle of approach,the easier it is for the natural fracture to be opened;when two intersecting natural fractures exist,the natural fracture is more likely to be opened when the second natural fracture is between the direction of the maximum horizontal principal stress and the direction of the first natural fracture;when the natural fracture is extensively developed and the horizontal ground stress difference is low,the hydraulic fracture expands forward along the natural fracture.The higher the fracturing fluid discharge and the lower the viscosity,the more conducive to the formation of complex fracture networks.