Gas hydrate dissociation of CO2-CH4 mixtures in porous media with sodium chloride – A fundamental basis for prediction of carbon capture in gas hydrates reservoirs

Abstract

Background: The rising atmospheric CO₂ levels, driven primarily by growing global energy demands, pose urgent climate challenges. In support of the International Energy Agency's ambitious carbon reduction goals, this study investigates CO₂/ CH₄ hydrate systems as a potential carbon capture solution. We specifically examine hydrate behavior under conditions mimicking deep-sea environments, with particular attention to sodium chloride's influence.

Methods: Laboratory experiments employed a high-pressure system to analyze CH₄ and CO₂ hydrate equilibrium conditions in reservoir rock samples featuring 20 nm pores. The isochoric pressure-search method was applied to perform tests in saltwater solutions (3.5% NaCl). Key parameters—including concentration, pressure, and temperature—were rigorously controlled to accurately simulate hydrate formation and dissociation processes.

Significant Findings: It was observed that increasing CO₂ levels reduce the equilibrium pressure of CH₄ + CO₂ mixtures. The thermodynamic model used exhibited a strong predictive ability with an average absolute deviation of 3.38%. It was found that in nanopores (<20 nm), capillary forces govern hydrate formation while salinity effects become marginal, as evidenced by comparative water/salt system analyses. The study highlights the role of pore size, water salinity, and capillary pressures on hydrate stability, which are critical for improving CO₂ sequestration methods and advancing natural gas recovery techniques.