A Life-Cycle-Oriented Critical Production Drawdown Model for Weakly Consolidated Bohai Sandstone Reservoirs Under Coupled Water-Induced Weakening and Pore-Pressure Depletion

Weakly consolidated sandstone reservoirs in the Bohai region are susceptible to sand production and wellbore instability during high-water-cut production because water–rock interaction progressively degrades rock strength while reservoir depletion increases effective stress. This study proposes a time-dependent critical production drawdown framework that couples water-induced weakening with pore-pressure depletion. Laboratory soaking data are mapped to field production through a cumulative equivalent soaking time weighted by water cut and operating time. Time-dependent cohesion, friction angle, elastic modulus, Poisson’s ratio, and uniaxial compressive strength are updated by interpolation, while pore pressure and poroelastic/thermoelastic stresses around an inclined wellbore are updated synchronously. The Mohr–Coulomb criterion is used to identify the critical bottom-hole flowing pressure. For the investigated sandstone, soaking from 1 to 7 d reduced cohesion from 15.32 to 12.36 MPa, friction angle from 24.57° to 19.21°, and elastic modulus from 7.49 to 1.85 GPa, while Poisson’s ratio increased from 0.363 to 0.433. The allowable production drawdown decreased from 8.119 to 1.289 MPa, an 84.1% reduction, with an operational 90% confidence interval of 50–100%. Cohesion dominates the absolute response range, whereas on a per-unit-relative-change basis, pore pressure, well inclination, and friction angle become comparable or larger controls. The framework supports dynamic drawdown control, sanding-risk assessment, and sand-control optimization over the production life cycle. It was benchmarked against a 259-day sand-free producing well and two published Bohai sand-onset case studies; the comparison is indicative, and field-history calibration of the equivalent soaking time remains a priority for future validation.