Drilling- and Reservoir-Constrained First-Order Probabilistic Assessment of Gas Hydrate Stability and Slope Sensitivity in the Shenhu Production Area, Northern South China Sea

This study develops a MATLAB-based (MathWorks, Natick, MA, USA; version R2024b) first-order probabilistic screening framework for the Shenhu gas hydrate production area, northern South China Sea, to separate the roles of bottom-water warming, geothermal and fluid perturbation, hydrate saturation, excess pore pressure, and slope geometry. The framework integrates methane hydrate phase equilibrium, geothermal profiles, transient heat diffusion, base of gas hydrate stability zone (BGHSZ) migration, conceptual reservoir phase layering, and infinite-slope factor-of-safety (FoS) analysis. The modeled present-day BGHSZ (~271 mbsf) is broadly consistent with reported bottom-simulating-reflector depths. At the baseline thermal diffusivity, conductive potential dissociation thickness stays below 4 m even for +3.0 °C over 1000 years; across the full tested diffusivity–warming–time matrix it ranges 0–19.5 m; geological tests, reported as equilibrium BGHSZ offsets, give larger responses. Monte Carlo analysis under three parallel slope-angle assumptions shows that absolute FoS depends strongly on the slope distribution. Conductive warming reduces the median FoS by about 5.5%, with about 9% of realizations exceeding a 10% reduction, yet low-FoS outcomes remain absent within the tested ranges. Within the adopted parameterization, modeled FoS variability is controlled primarily by slope angle, friction angle, and the prescribed excess pore-pressure ratio, while conductive thermal forcing produces a comparatively modest reduction in relative stability margin.