The depressurization of natural gas hydrate in the multi-physics coupling simulation based on a new developed constitutive model

Abstract

Natural gas hydrate has become a hotspot for researchers because of its considerable economic benefits and potential strategic significance. In the hydrate exploitation process, the hydrate-bearing sediments get damaged, and the coupling effect of multi-physical fields is involved. In this study, a damage constitutive model of hydrate-bearing sediments is established by considering decomposition damage, loading damage, and the influence of residual strength. Based on this damage constitutive model, a Thermo-Hydro-Chemo-Mechanical (THCM) multi-field coupling model considering the sediment damage is constructed on the COMSOL simulation platform. Compared with the experimental data, the THCM coupling model is demonstrated and employed to study the depressurization process of horizontal wells in permafrost regions. During the hydrate exploitation model, changes in displacement, saturation, average pore pressure, and temperature at different mining positions are recorded and analyzed. The results indicate that the damaging of sediments has a significant effect on soil deformation and temperature. After the sediment damaging effect is considered, the minimum temperature of the extraction points is reduced by 22.5% at most. The maximum deformation of the extraction points is about 11.8% greater than that without considering the sediment damage effect. Moreover, the model reveals the self-preservation effect of gas hydrate. The temperature of the surrounding soil at the exploitation site decreases due to hydrate decomposition, which would inversely promote hydrate formation. These numerical models in this study can be applied to estimate the strength of sediments and predict the reservoir settlement in the process of hydrate depressurization.