Borehole instability, sand production, and completion failures during production and pore pressure depletion continue to be significant problems confronting the petroleum industry. This study develops quantitative models for predicting borehole shear failure in pressure-depleted and repressurized reservoirs by incorporating stress path into equations for shear of borehole wall rock. Critical reservoir pore pressure (CRPP) is defined as the pore pressure below which any drawdown or additional pore pressure depletion will result in the onset of borehole shear failure. Critical reservoir pore pressure and critical borehole pressure (CBHP) are defined in terms of initial stress state, initial reservoir pore pressure, the two horizontal principal stress paths, and commonly used failure criteria. The model includes both overbalanced (drilling) and underbalanced (production) scenarios. The model is applicable to both vertical and horizontal wells.