Reliability analysis of submarine slopes in hydrate extraction by depressurization-assisted replacement

As an extension of CO2 replacement method, the depressurization-assisted replacement method can improve extraction efficiency. For these two methods, this paper takes the hole GMGS2-08 as a case study. By integrating infinite slope model and random field theory, this text analyses the impact of three factors on the slope safety, such as the strength differences from different hydrate types and saturations, the strength discounting due to the earthquake, and the seismic addition force. And, the impact degree of the three factors increases in sequence. In the non-stationary random field, this paper sets cohesion (c), friction angle (phi), unit weight (gamma) and reduction coefficient (xi) as four random variables. There is found that the correlation between the c and phi, the cohesion variability, the friction angle variability, the reduction coefficient variability, the cohesion trendiness, the friction angle trendiness, and the unit weight trendiness have a more important impact on the failure probability (Pf) of submarine slops. When the Pf is about 65%, the safety factors with different slopes angles are around 1.05, despite the different effects of seismic forces and strength discounting. The combined analysis of safety factor and the Pf can offer excellent early warning for safe hydrate extraction.