Pore-scale behaviors of CO2 hydrate formation and dissociation in the presence of swelling clay: Implication for geologic carbon sequestration

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Hydrate-based CO2 sequestration (HBCS) under seafloor with huge storage capacity and long-term mechanical stability is attractive for large-scale carbon reduction. However, as representative geochemical constituents of marine sediments, swelling clay minerals still play ambiguous roles in hydrate phase transition and sedimentary structure stability. In this study, pore-scale behaviors of hydrate deposition and reservoir structure evolution in the presence of montmorillonite (MMT), a representative swelling clay, was investigated using low-field nuclear magnetic resonance (LNMR) technique. Total inter-particle interaction energy of 195.4 KbT ensured the dispersion of clay in 0.5 wt% MMT system, which facilitated homogeneous hydrate formation by providing nucleation sites and surface electric fields, improving hydrate conversion from 78.2 % to 89.6 %. Weak water activity caused by strong water absorption of swelling clay resulted in a 14.4 % reduction in CO2 storage capacity of high-concentration (10.0 wt%) MMT reservoir. Hydrate phase transition accompanied by the migration of MMT particles and liquid water synergistically contributed to sedimentary structure evolution. Migration of MMT-rich fluid with high viscosity could cause irreversible geologic damages by exacerbating sedimentary skeleton deformation. This work reveals the interaction between swelling clay and CO2 hydrate at microscopic scale, providing new perspectives for effective implementation of CO2 geologic sequestration in marine sediments.