Non-equilibrium hydrate kinetics induced by swelling-deswelling dynamics in clay matrices

Natural gas hydrates (NGHs), predominantly composed of methane, represent a vast carbon reservoir and a potential energy resource, particularly in clay-rich marine sediments. However, their destabilization poses serious environmental risks, including methane release, seabed subsidence, and ecosystem disruption. While previous studies have primarily focused on NGHs in sandy sediments, the role of clays remains poorly understood. Smectite clays exhibit complex swelling behavior, including osmotic swelling that allows substantial interlayer expansion and may fundamentally alter hydrate formation pathways. Recent field observations of anomalously low large-to-small cage occupancy ratio (θ LC /θ SC ) in smectite-rich sediments further suggest a potential influence of clay mineralogy on NGHs. In this study, we investigated methane hydrate growth in clay matrices using a combination of neutron diffraction and Raman spectroscopy. We provide direct experimental evidence of hydrate formation within swelling clays, demonstrating that cyclic interlayer swelling and deswelling induce localized mass transfer limitations, which fundamentally alter hydrate growth kinetics and cage occupancy. These results reveal a distinct, non-equilibrium hydrate formation regime in swelling clays, highlighting the need for accurate prediction of CH 4 recovery yields and geological CO 2 storage capacities that account for mineral-specific transport constraints, rather than relying on idealized models.