Numerical Assessment of Gas Hydrate Dissociation on Submarine Slope Stability-Paper

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The study numerically assesses how heating from an offshore production well can dissociate gas hydrates in a 5° submarine slope and affect sediment strength and slope stability. Hydrate dissociation releases water and gas, potentially raising pore pressure, reducing effective stress, and weakening the sediment.<br /><br />The analysis uses the HYDRATERESSIM simulator to model heat flow, hydrate dissociation, and excess pore pressure, then estimates shear-strength reduction and slope factor of safety with GeoStudio Slope/W. The model represents a well maintained at 82°C for up to 20 years.<br /><br />In the base case, the dissociation front generally extends no more than about 30 m from the well. Sediment failure is localized near the well, typically within about 40 m, with a wider affected zone in the deepest layer. The slope’s factor of safety decreases from 3.11 before production to 2.98 after five years and 2.92 after 20 years. The modeled dissociation does not trigger seafloor slope failure.<br /><br />Sensitivity analyses show that lower thermal conductivity and higher pore compressibility noticeably affect excess pore pressure and the extent of sediment failure. The authors therefore emphasize the need for reliable parameter estimates. Importantly, the stability analysis includes weakening from dissociation-induced excess pore pressure but does not account for the loss of hydrate’s cementing effect on sediment strength. This omission means the modeled impact on slope stability may not capture all potential weakening mechanisms.

Keywords

gas hydrates

offshore production well

submarine slope stability

hydrate dissociation

excess pore pressure

sediment strength reduction

slope factor of safety

HYDRATERESSIM

GeoStudio Slope/W

sensitivity analysis