Experimental study of gas recovery behaviors from methane hydrate-bearing sediments by CO2 replacement below freezing point

Natural gas hydrate (NGH) is one of the most promising clean energy sources in the future because of its huge reserves and cleanliness, and the CO2 replacement method can realize the safe extraction of NGH and the un-derground storage of greenhouse gases. This study investigates the influence of quartz sand size and ice content on hydrate replacement characteristics below freezing point conditions. Results indicate that, at a temperature of 271.65 K, when particle sizes range from 250 mu m to 500 mu m, there is an observed increase in CH4 recovery alongside a concurrent decrease in CO2 sequestration as particle size decreases. Additionally, when maintaining a fixed 500 mu m particle size, the proportion of quartz sand positively correlates with CH4 recovery. Furthermore, the presence of quartz sand grains in an ice powder system can improve the replacement effect. By contrast, the presence of quartz sand significantly enhances the CO2 sequestration ratio more than the CH4 recovery ratio. In mixed ice-sand porous media, CO2 sequestration can be enhanced from 0.0496 mol to 0.1012 mol, representing a 104 % increase in CO2 sequestration molarity when compared to the pure ice conditions.