Numerical study failure characteristics of natural fracture under induced stress

Abstract

Hydraulic fracturing is an effective method for developing oil and gas in unconventional reservoirs. The openings of natural fractures directly affect the complexity of the fracture body. The failure characteristics of natural fractures are critical factors in determining their activation by hydraulic fractures. Based on the three-dimensional displacement discontinuity method, a three-dimensional mechanical model of the interaction between hydraulic and natural fractures was established. Based on the shear and tensile failure criteria of the natural fractures, the failure characteristics of different natural fractures were clarified. Research has shown that the failure characteristics of natural fractures are influenced by factors such as three-dimensional stress, spatial distribution, and roughness. After the hydraulic fractures pass through the natural fractures, tensile and shear failures occur simultaneously; the failure of natural fractures is primarily affected by their strike and dip angles. During the process of hydraulic fracture approximation, the shear stress increases as the distance between the hydraulic fracture tip and natural fracture decreases. When the strike angle of the natural fractures near the tips of the hydraulic fractures was greater than 35°, the stress became consistent. As the dip angle of the natural fractures increased, the lowest point of the shear stress gradually moved from the upper to the lower half. This research studies the tensile and shear failure of natural fractures under different conditions, in order to facilitate engineering judgment of the types and characteristics of natural fracture failure. It is of great significance for us to understand the formation mechanism of complex fracture network morphology in volume fracturing.