Multi-fracture propagation and deflection laws of horizontal wells in tight sandstone

In order to study the multi-fracture slotted propagation and deflection laws of horizontal wells in tight sandstone, the influences of crack spacing, main stress difference and discharge capacity on the propagation geometry of multi-fractures are studied by using physical experiments and numerical simulations with FLAC^3D based on four-dimensional water jet slitting device and large-scale true triaxial hydraulic fracturing simulation system. A stress filed theoretical model of opening single and multi-fracture with water pressure and a set of indoor slotting-fracturing physical test method are established. The analysis of the characteristics of the sample splitting and the pressure curve reveals: (1) The typical fluctuation peak of the subsequent pressure curve after the initiation cracking is an obvious feature of the fracture mutual stress interference. The short spacing makes the adjacent fracture in the high induced stress zone, leading to strengthening the stress mutual interference and the degree of fracture deflection. (2) The angle and extent of the multi-fracture deflection increase greatly due to the high-volume pump increasing the internal water pressure of the fracture and short spacing, which forms the longitudinal hydraulic fracture. The middle fracture restrained nearly propagates in the direction perpendicular to the maximum principal stress and tends to stop propagating, while the extending distance between the middle fracture at both sides is longer. (3) The deflection angle declines because the induced stress is too difficult to change the original the stress field under the high stress difference. The subsequent propagation fluctuation is relatively stable, and the fracture is more likely to form a transverse hydraulic fracture parallel to the direction of the maximum principal stress. The research results can be used to optimize the design parameters of slotting multi-fracture and provide technical reference for oil and gas exploitation of sandstone reservoirs under different geological conditions and hydraulic fracturing of hard roof in coal mines to control the strong mine pressure.