A new approach to high conversion CO2 hydrate sequestration by CO2/water emulsion injection into marine sediments

Hydrate-based CO 2 storage is a highly promising technology for long-term stable CO 2 storage in sediments. However, the unclear displacement and hydration mechanisms, along with the low conversion rate of CO 2 hydrates, have hindered the field application. Here, we report a method of the injection of CO 2 /water emulsion to replace liquid CO 2 to regulate the ratio of CO 2 to water in the sediment pores and to enhance their contact ability, which can significantly improve the CO 2 hydrate conversion rate. Compared to liquid CO 2 injection, emulsion injection can flow through more sediment pores with an increase in displacement efficiency by 45 %-62 %, which leaves a CO 2 -to-water ratio within the pores that is more suitable for hydrate formation, ultimately tripling the hydrate conversion rate. We have outlined the hydrate growth mechanisms for both injection forms, where the micron-sized CO 2 droplets within the emulsion can greatly reduce the barrier effect of hydrate film. Under the combined influences, the CO 2 storage density in hydrates up to 91.2 kg/m 3 for CO 2 /water emulsion injection is 47.8 % higher than that of 61.7 kg/m 3 for liquid CO 2 injection. Our work provides a new approach to high conversion CO 2 hydrate sequestration in submarine sediments.