Wellbore instability and sand production pose critical challenges in deep tight sandstone reservoirs, severely impairing wellbore integrity and reducing hydrocarbon recovery. This study introduces, for the first time, the combined finite–discrete element method (FDEM) to numerically simulate sand production under high in situ stress. The FDEM By seamlessly integrates continuum and discontinuum representations within a unified framework, enabling the simulation of the complete failure sequence—from matrix damage and fracture growth to granular flow. High-resolution numerical simulations are conducted to compare intact and naturally fractured formations, with a focus on the governing role of pre-existing geological discontinuities. Results show that in intact sandstone, stress concentration drives helical crack growth leading to a symmetrical V-shaped breakout, with a critical borehole pressure (CBHP) of 60.05 MPa required to prevent instability. In fractured rock, however, pre-existing fractures act as dominant weakness planes that distort the stress field and induce earlier, asymmetric failure, raising the CBHP to 64.05 MPa. A strong negative linear correlation is observed between reservoir pressure depletion and CBHP: a pore-pressure reduction of 23.75 MPa decreases the CBHP by 4.8–5.0 MPa. Notably, natural fractures amplify the destabilizing effect of depletion, raising the required CBHP by 4.0 MPa at initial reservoir pressure (95 MPa) and by 5.0 MPa under full depletion. Consequently, although fractured formations require a higher CBHP (64.05 MPa vs. 60.05 MPa), their safe operating window is effectively narrower. These findings advance the mechanistic understanding of fracture-controlled sand production and provide a validated numerical framework for determining safe production pressures in deep, fractured sandstone reservoirs.
Zhang et al. (2026) studied this question.