Geomechanical Response Analysis of Gas Hydrate Extraction Using CO2 Hydrate Sealing Burdens

During the process of natural gas hydrate (NGH) depressurization exploitation, the intrusion of formation water makes the pressure drop propagation difficult and the gas production lower. At the same time, the decomposition of hydrate in the pore space reduces the cementing strength of the formation, which may lead to geologic hazards such as seafloor subsidence and seafloor landslides. Utilizing CO2 hydrate to seal the overburden of NGH reservoirs not only prevents intrusion of formation water and improves gas production, but also achieves CO2 sequestration. In previous studies, only the gas production increasing was analyzed and the response of the geomechanics during the gas production process was not paid enough attention. In this paper, A coupled thermal–hydraulic–mechanical–chemical (THMC) model for CO2 hydrate sealing of overburden is established by using numerical simulation. Gas production and geomechanical response during the production with sealing overburden were analyzed; The results show that sealing the overburden can effectively promote the propagation of the pressure drop of the CH4 hydrate layer and the supplementation of heat during the production. Sealing overburden can effectively increase the cumulative gas production, decrease the water production, and reduce the seafloor subsidence. Exploiting gas hydrate with sealing overburden is conducive to realizing the dual goals of efficient production and safe production. This work can provide a reference for better realization of safe and efficient production of natural gas hydrate.