Artificial Fracture Deflection And Propagation Mechanism Based On Phase Field Method

The tight reservoirs is low porosity,low permeability and have many natural fractures.so hydraulic fracturing technology is generally used for exploitation.In the process of hydraulic fracturing,the artificial fracture firstly deflect and propagate in the area near the wellbore under the influence of in-situ stress,and then it communicate with the natural fractures in the reservoir to form complex fractures.However,the directions of natural fractures in tight reservoirs are diversified.Natural fractures with different directions will affect the propagation of artificial fractures,resulting in insufficient communication between artificial fractures and natural fractures,and affecting fracturing effects.Therefore,studying the deflection and propagation Mechanism of artificial fractures during hydraulic fracturing is of great significance for the rational use of natural fractures in tight reservoirs and improving the effect of hydraulic fracturing.However,current numerical simulation methods of hydraulic fracturing,such as Cohesive zone,XFEM,etc.,are difficult to simulate the fracture deflection and intersection at the same time.Aiming at the above problems,this paper establishes a hydraulic fracturing model of fluidsolid coupling in linear elastic porous media based on the basic principles of the fracture phase field method.Simulating the deflection and propagation behavior of artificial fractures under the influence of construction parameters and natural fractures.A new idea of controlling the intersection angle of artificial fractures and natural fractures by perforating direction is proposed to improve the complexity of hydraulic fracturing of tight reservoirs to provide theoretical basis for improving the effect of hydraulic fracturing of tight reservoirs.The main work and results are as follows:(1)The basic principle of the fracture phase field method is explained,and on this basis,the influence of the porous medium fluid on the artificial fracture propagation is introduced,the fluid-solid coupling hydraulic fracturing model is established,and the accuracy of the model is verified.(2)A fracturing propagation model of artificial fractures near the wellbore was established to simulate the mechanical behavior of artificial fractures propagation under construction parameters.It can be seen from the simulation results that the perforation azimuth will affect the deflection angle of the artificial fracture.The greater the angle between the artificial fracture and the maximum horizontal principal stress,the greater the deflection angle.The horizontal ground stress difference of the reservoir will affect the deflection speed of the artificial fracture.The higher the horizontal ground stress difference,the faster the deflection speed to the direction of the maximum principal stress when artificial fractures propagate.During hydraulic fracturing,the perforation direction can be set according to the in-situ stress of the reservoir to control the deflection and propagation of artificial fractures.(3)An artificial fracture propagation model containing natural fractures is established,to simulating the propagation behavior of artificial fractures when the reservoir contains natural fractures.And analyzing the influence of the angle between natural fractures and the horizontal in-situ stress difference of the reservoir on the deflection and propagation of artificial fractures.The simulation results show that the reservoirs with the horizontal stress difference of 4 to 5MPa and the angle about 75° between artificial fractures and natural fractures,hydraulic fracturing has a better effect.The above research results deeply reveal the deflection and propagation mechanism of artificial fractures in tight reservoirs,and provide theoretical support for improving the effect of hydraulic fracturing.