Experimental study on the stability of CO2 hydrate in submarine sediments environment

Hydrate-based CO2 storage represents a compelling strategy for CO2 oceanic storage. The long-term stability of CO2 hydrates is the pivotal indicator for assessing the technical viability of this strategy. Investigation on CO2 hydrate stability can not only quantify the risk of CO2 leakage to the environment, but also provide the mechanistic basis for optimizing long-term, secure storage. The hydrate dissolution rate serves as the quantitative proxy for hydrate stability. Accurate quantification of CO2 hydrates dissolution rates in marine settings is therefore imperative. This study presents a comprehensive, 200-hour experimental program to quantify the dissolution rate of CO2 hydrate under submarine sediments environment. The porosity and true density of the reconstructed sediment used were 45% and 2.8 g/cm3, respectively. Factors such as temperature, pressure, and sediment cap thickness were investigated to determine the dissolution rate of CO2 hydrates under different conditions. The dissolution rate of CO2 hydrates increases modestly with rising temperature and pressure, yet declines precipitously as sediment cap thickens. Across the investigated parameter space, the dissolution rate spans 4.87–134.73 cm/year. In diffusion-controlled hydrate dissolution, the sediment cap dramatically suppresses the CO2 molecular diffusion flux by simultaneously lowering porosity and increasing tortuosity. Over long-term evolution, once the local temperature and pressure conditions are established, the sediment cap thickness emerges as the predominant factor controlling the hydrate dissolution rate. These findings provide a mechanistic basis for assessing the long-term stability of CO2 hydrates during storage and offer critical guidance for the design of enduring CO2 hydrate storage strategies.