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

Hydrate-based CO2 storage is a highly promising technology for long-term stable CO2 storage in sediments. However, the unclear displacement and hydration mechanisms, along with the low conversion rate of CO2 hydrates, have hindered the field application. Here, we report a method of the injection of CO2/water emulsion to replace liquid CO2 to regulate the ratio of CO2 to water in the sediment pores and to enhance their contact ability, which can significantly improve the CO2 hydrate conversion rate. Compared to liquid CO2 injection, emulsion injection can flow through more sediment pores with an increase in displacement efficiency by 45 %-62 %, which leaves a CO2-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 CO2 droplets within the emulsion can greatly reduce the barrier effect of hydrate film. Under the combined influences, the CO2 storage density in hydrates up to 91.2 kg/m3 for CO2/water emulsion injection is 47.8 % higher than that of 61.7 kg/m3 for liquid CO2 injection. Our work provides a new approach to high conversion CO2 hydrate sequestration in submarine sediments.