Study on the guiding mechanism of controlling pore water pressure on the propagation path of hydraulic fractures

Abstract

Aiming at the difficulty in controlling fracture propagation direction during coal seam hydraulic fracturing, this study establishes a pore water pressure-regulated fracture propagation control model via theoretical analysis, numerical simulation, and experimental verification, revealing regulatory laws of lateral stress coefficient, control hole position, water injection pressure, and spacing on fracture deflection. Results show fracture propagation features ’ initial directional initiation followed by gradual deflection ’, with propagation-required water pressure decreasing as fracture length increases. For lateral stress coefficient λ > 1, fracture deflection angle decreases from 45° to 11.25° with increasing λ; for λ < 1, it drops from 45° to 7.5° as λ decreases. At λ = 1, fractures propagate linearly along the inter-hole line. The oblique hole is the optimal turning point: in λ > 1 formations, deflection angle ’ first increases then decreases ’ with β increasing; in λ < 1 formations, it shows the same trend as β decreases. A smaller hole spacing leads to significant early deflection of fractures. A higher pore pressure in the control hole results in an increased fracture deflection angle, along with enhanced pore water pressure at the midline connecting the two holes and a greater amplitude of fracture deflection. The fracture path is synergistically controlled by the pore water pressure gradient and the in-situ stress field. Simulations align with relevant physical experiments, validating the theoretical model. The findings provide a theoretical basis for directional fracture propagation via optimized control hole parameters in coal seam hydraulic fracturing.