Enhanced CO2 injection and hydrate conversion in unsealed submarine sediments for CO2 hydrate sequestration by CO2-H2O emulsion injection

CO₂ hydrate provides an important alternative solution for CO₂ geological sequestration. However, fingering flow of liquid CO₂ and hydrate membrane effect can severely restrict flowing CO₂ conversion to hydrate. Here we report an enhanced CO₂ hydrate sequestration method via CO₂-H₂O emulsion injection, and its effectiveness has been proven in a three-dimensional system. Compared to liquid injection, emulsion injection demonstrated higher displacement efficiency of pore water and larger sweep area, finally increasing CO₂ sequestration density by 142 %. The highly dispersed CO₂ micro-droplets significantly increase CO₂-H₂O contact capability and weakens the hydrate membrane effect, thereby greatly increasing the rate and quantity of hydrate conversion. For different water contents, the highest CO₂ sequestration density of 148 kg/m³ is achieved at 40 % water content, with hydrated CO₂ accounting for 71.45 %. The excellent performance of CO₂-H₂O emulsion provides a green and high-efficient approach to CO₂ hydrate sequestration.