Experimental Study on the CO2 Hydrate Sequestration Capacity in Muddy Siltstone Reservoirs at Different Burial Depths

Hydrate-based carbon sequestration is a highly promising and innovative technology, this study investigates the sequestration characteristics at different simulated ocean depths from an experimental perspective. The experiments were conducted using a self-constructed high-pressure visual reactor, aiming to provide theoretical insights into the sequestration mechanism and engineering application of hydrate-based carbon storage. In this study, a self-designed high-pressure visual reactor was employed to simulate the real high-pressure environment of the ocean using a water pressure of 8 MPa. Marine muddy silt was selected as the CO2 storage medium to represent marine sediment, and the thermodynamic conditions corresponding to different burial depths were simulated. We investigated the CO2 storage capacities of sediment layers at simulated ocean depths of 1530–1675 m, 1570–1730 m, and 1630–1730 m. The results indicate that CO2 tends to form hydrates more readily in the sediment layer at a depth of 1570–1730 m, achieving a final storage capacity of 220 g liquid CO2 with a storage efficiency of 50%. We found that the leakage behavior and rate of liquid CO2 are closely related to the formation of hydrates within the reservoir. After 62 min of injection, CO2 began to leak from the reservoir. At 200 min, hydrate formation was initiated and gradually accumulated within the pore channels, resulting in a transition of the CO2 leakage pattern from continuous small bubble release to intermittent large bubble emission. Consequently, the leakage rate decreased from 1.4 g/min to 0.6 g/min as the flow channels became partially blocked. After 450 min of injection, when the leakage rate reached its minimum value of 0.2 g/min, a dense hydrate cap had largely developed within the reservoir, significantly constraining the seepage pathways. At this stage, the escaping CO2 bubbles were observed to be encapsulated by thin shell-like hydrate films, and their rising velocity was notably reduced.