Dynamic Coupling of Hydrate Decomposition and Wellbore Stability in Horizontal Drilling: Experimental and Numerical Insights for Safe Gas Hydrate Extraction

Horizontal drilling in gas hydrate reservoirs faces critical wellbore instability challenges due to dissociation-induced sediment weakening. This study integrates large-scale experiments with validated numerical simulations to reveal the governing mechanisms of wellbore failure. High-pressure reaction kettle experiments demonstrate that drilling fluid temperature dominates stability: increasing temperature from 20 to 40 °C accelerates collapse by 30–40%, reducing collapse time from 5.21 to 4.89 days. Monte Carlo sensitivity analysis confirms that temperature controls 58% of plastic strain variance, while borehole size and initial saturation account for 12% and 22%, respectively. Critically, we establish that maximum plastic strain at the wellbore wall─not hydrate dissociation rate alone─determines failure timing, with strain exceeding 0.05 triggering collapse. This mechanistic insight explains why larger boreholes, despite inducing wider dissociation zones, show a lower strain concentration and enhanced stability. A multivariate predictive model ( R 2 = 0.952) successfully captures the coupled parameter effects, confirming temperature’s dominant role while revealing saturation’s significant stabilizing influence. Numerical simulations demonstrate that optimal drilling conditions─particularly maintaining fluid temperature 2–5 °C above phase equilibrium. These quantitative relationships provide actionable guidelines for designing safe drilling operations, establishing plastic strain monitoring as a critical real-time stability indicator for commercial hydrate extraction.