Multiscale Study on Shallow CO2 Sequestration via Winter Natural Cold Energy: From Zeolite-Mediated Hydrate Kinetics to Field-Scale Simulation

Utilizing winter natural cold energy for shallow CO2 hydrate sequestration offers a sustainable, energy-efficient pathway for carbon neutrality. However, the upscale application of this technology requires a comprehensive understanding of both microscopic host-sediment interactions and macroscopic reservoir performance. This study integrates laboratory experiments with field-scale numerical simulations to evaluate the feasibility and safety of storing CO2 in zeolite-bearing sediments under seasonally frozen conditions.

In the experimental phase, a visualized high-pressure reactor was employed to investigate CO2 hydrate formation and dissociation characteristics across three sediment types: quartz sand, montmorillonite, and zeolite. Influencing factors including particle size, water saturation, and diverse P-T conditions were systematically analyzed. Results quantified that zeolite sediments significantly outperformed traditional media, shortening the hydration induction time by 17.6% and increasing gas storage capacity by 21.3% compared to quartz sands. This enhancement is attributed to the "molecular sieve" effect and high specific surface area of zeolite. Microscopic characterizations using NMR, XRD, and SEM further revealed that the unique microporous framework of zeolite provides abundant nucleation sites and exerts a strong self-preservation effect, which prolonged the hydrate dissociation window by over 1.20 hours at -5°C, providing a critical safety margin against accidental thermal fluctuations.

Complementing the laboratory findings, a field-scale reservoir model was constructed using the CMG software to simulate the long-term injection and storage process in a pilot area in Northeast China. The simulation coupled thermal-hydraulic-chemical (THC) processes to predict the evolution of the temperature field and the spatial distribution of the hydrate stability zone. Simulation results indicated that utilizing natural cold energy (ambient air temperature of -20°C) could sustain a stable HSZ with a radius of 200 meters around the wellbore. Furthermore, the model validated that the exothermic heat of hydration was effectively dissipated by the continuous cold energy supply, preventing thermal instability. Sensitivity analysis within CMG demonstrated that the leakage risk in zeolite-rich layers was reduced by 15.89% compared to conventional aquifers due to the dual trapping mechanism of solid hydrate formation and adsorptive trapping.

This study elucidates the coupled mechanism of "Cold Energy Drive + Zeolite Enhancement", confirming that zeolite is an ideal functional medium for shallow CO2 sequestration. The findings provide robust theoretical support and quantitative design parameters for implementing low-cost CCS projects in cold regions.

Keywords: CO2 Sequestration; Natural Cold Energy; Zeolite; CMG Simulation; Self-preservation; Multiscale Analysis