Stability Analysis of Submarine Hydrate-Bearing Slope During Depressurization Production

Abstract South China Sea hydrate reservoirs, mostly weakly cemented silty sandstones, are prone to landslides during extraction. Prior studies have inadequately considered factors such as dynamic decomposition of hydrates during depressurization, and the impacts on the reservoir's geomechanical properties. In this paper, a coupled thermal-hydraulic-mechanical-chemical mathematical model of hydrate decomposition is proposed, and the dynamic geomechanical response and the effect of hydrate decomposition on seafloor settlement and slope destabilization in the process of depressurization mining are analyzed by combining the strength discount method. The results show that hydrate decomposition is non-uniform due to stratigraphic temperature gradients and gravity. In hydrate depressurization zones, a decrease in pore pressure leads to increased effective stress. Simultaneously, hydrate decomposition reduces the shear modulus of sediments, causing deformation and decreased permeability in the decomposition area. During three years of depressurization mining, the stability coefficient of hydrate-bearing slopes decreased from 1.66 to 1.41, and the maximum settlement increased to 0.864 meters, raising landslide risks. The research results have significant guiding implications for the safe exploitation of hydrate-bearing slopes.