Evaluation of carbon sequestration stability based on ice-hydrate coupling effect in ice lenses covered permafrost regions

Implementing carbon sequestration in permafrost regions using hydrate technology offers a promising strategy for long-term carbon storage. Ice phases in permafrost play a critical role in regulating hydrate decomposition kinetics and sequestration stability. This study, for the first time, proposes and validates a stability-enhancement strategy that exploits these ice phases, progressing from pore-scale analysis to ice lens-covered reservoirs representative of natural permafrost heterogeneity. Using low-field NMR and visualization experiments, we examine hydrate phase-transition responses under heating (−5 to 5 °C), depressurization (0.9 MPa to atmospheric pressure), and varying ice cap thicknesses (0–2.5 cm). Results show that regenerated pore ice formed during heating inhibits hydrate decomposition, an effect amplified by ice lens structures. Ice-induced gas diffusion suppression and heat transfer between ice and hydrates prolongs sequestration duration by up to 231.9 min and increases retained sequestration capacity by 31.8%±1.15%. Moreover, the instability threshold of hydrate sequestration is critically controlled by asynchronous deformation between ice and hydrate phases in conjunction with pore structure characteristics. This study elucidates the pore-scale structural evolution during instability in ice-hydrate reservoirs, providing new insights into stability regulation mechanisms for hydrate-based carbon sequestration in permafrost regions and establishing a theoretical basis for optimizing sequestration engineering designs.