Dependence of the hydrate-based CO2 storage characteristics on sand particle size and clay content in unconsolidated sediments

Storing carbon dioxide (CO2) in the form of hydrate in marine sediments is considered an effective way of carbon reduction. Understanding the influence of sediment properties on CO2 hydrate formation is important for the site selection of CO2 hydrate storage in marine sediments. In this study, the effects of sand particle size and bentonite content on the kinetics of CO2 hydrate formation are analyzed using low-field nuclear magnetic resonance technology, and the hydrate-based liquid CO2 storage capacity is evaluated. Results show that CO2 hydrate forms preferentially in large pores of sand samples, the water content in small pores begins to decrease before the hydrate saturation reaches 20%, and the unhydrated water mainly concentrates in small pores. With the increase of sand particle size, the CO2 storage rate of the early rapid growth stage increases first and then decreases, the CO2 storage rate of the whole hydrate formation process decreases continuously, but the final CO2 storage density is weakly affected by sand particle size. With the increase of hydrate saturation, the CO2 storage rate undergoes a trend of rapid decrease, stability, rapid decrease, and low-speed decrease in sequence. The larger the sand particle size or the higher the bentonite content, the shorter the stability stage of CO2 storage rate. The effect of bentonite on CO2 storage rate is the promotion at low content, the inhibition at medium content, and the weakening of inhibition at high content. The sediments with more than 25% bentonite are beneficial to the storage of more CO2.