Dynamic stability evaluation of submarine slopes with hydrate reservoir under influences of heat injection exploitation

The heat injection exploitation will destroy the temperature and pressure balance of hydrate reservoirs, cause hydrate dissociation, lead to the dramatic increase of pore pressure of strata, and then induce the instability of submarine slopes along the hydrate reservoirs or even a large-scale submarine landslide. Therefore, it is very important to investigate the dynamic response of the hydrate reservoirs and the real-time stability of the submarine slopes after environmental changes. First, a solving equation for calculating the real-time excess pore pressure considering thermo-hydro-chemical (THC) coupling is derived, and the internal relation between the hydrate saturation and the excess pore pressure is also established. Further, a simplified evaluation approach for the dynamic stability of the submarine slopes under the influences of heat injection exploitation of the hydrate reservoirs is proposed based on the theory of infinite slope limit equilibrium analysis, and the corresponding numerical simulation and calculation code are developed. This approach is employed to analyze the submarine slope in the second hydrate extraction area on the northern continental slope of the South China Sea. The evolution characteristics of the submarine slopes in the process of heat injection exploitation of the hydrate reservoirs, such as the temperature profile, hydrate saturation profile and dynamic stability factors, are explored, and the reasonable mining suggestions are put forward. The research results provide an important basis for understanding the mechanism of instability of submarine slopes caused by hydrate dissociation, realizing the safe and sustainable development of the hydrate reservoirs and the scientific assessment of marine geological disaster risks.