Investigating the Fracture Initiation Mechanisms of High-Angle Well Fracturing in Deep Offshore Reservoirs

Fluid-driven fracture initiation and path selection in confined porous quasi-brittle media are strongly influenced by stress anisotropy and geometric boundary conditions. In this study, a cement-based analog material and a true-triaxial loading system were used to investigate how wellbore orientation and perforation geometry affect measurable fracture initiation and propagation responses in a high-angle-well fracturing context. The results indicate that in vertical wells, fractures consistently initiate along the direction of the maximum horizontal principal stress σ_H, with fracture pressure increasing alongside the perforation phase angle. In contrast, for directional wells, the fracture pressures are governed by a combination of the wellbore azimuth, perforation phase angle, and well deviation angle. When a directional well's azimuth is aligned with σ_H, its fracture initiation behavior resembles that of a vertical well. Conversely, when the azimuth is aligned with σ_h, fracture complexity and steering increase with the well deviation angle. Beyond a critical deviation angle, the fracture reorients to the vertical plane, resulting in a T-shaped fracture after stimulation. When the wellbore azimuth is misaligned with either principal horizontal stress direction, fracture steering typically occurs, although subsequent propagation generally follows σ_H. These findings provide controlled experimental guidance for stress-dominated fracture initiation and near-wellbore path selection in high-angle wells under conditions broadly similar.