One-dimensional analytical model for thermo-hydro-mechanical coupling behaviour of hydrates overlying layer during gas production

The production of natural gas from hydrates involves notable phase change within the hydrate-bearing sediments as well as induces strong thermo-hydro-mechanical (THM) coupling response within the overlying layer, which potentially leads to well instability and hazardous deformation. This study aims to shed some light on this issue by developing a one-dimensional analytical model. Parametric study was conducted with typical values being determined in accordance with those in the South China Sea (SCS). During the production process, simulations with different permeability all exhibit a continuous accumulating response of excess pore pressure (EPP) with strong oscillation. Thermally induced EPP accumulates near the bottom of the overlying layer, resulting in greater peak values of EPP in the lower part of the layer, which has significant impact on the stability of the mining wells. The temperature load is the dominant factor to determine the expansion of overlying layer. With greater permeability, the accumulation rate of thermal-induced pore pressure is close to the dissipation rate, which to some extent alleviates the expansion. The proposed model is expected to form the basis for studies regarding this issue, and the presented results provide useful implications for the development of improved gas production techniques for deep sea hydrates.