Experimental study on karst carbon sink under the coupling of solubility carbon pump and carbonate pump

This study investigates the CO₂ sequestration potential of carbonate reservoirs under the coupled effects of the solubility carbon pump and the carbonate pump,as well as its variation with burial depth. A highpressure autoclave system was used to simulate water-limestone-CO₂ interactions, reproducing karst processes under temperature and pressure conditions equivalent to depths of 200-1 200 m. The amounts of dissolved and mineralized CO₂ sequestered were measured. Based on the experimental data,a predictive model for CO₂ sequestration was established using Henry's law and the van't Hoff equation. This model was then applied to estimate the CO₂ storage capacity of a hypothetical depleted carbonate oil and gas reservoir with a volume of 5×10⁵ m³,a porosity of 10%,and a water saturation of 50%. The results indicate that increasing burial depth elevates reservoir pressure,which not only enhances CO₂ solubility but also accelerates carbonate rock dissolution,thereby reinforcing the synergistic effect of the two carbon pumps and improving carbon sequestration efficiency. As the depth increases to the point where CO₂ enters a supercritical state,both its solubility and the dissolution-precipitation dynamics within the system are further enhanced. In the hypothetical depleted reservoir, the total CO₂ sequestration, mineralized sequestration, and dissolved sequestration increased from 3. 23 t to 23. 97 t,from 2. 18 t to 18. 98 t,and from 1. 05 t to 4. 99 t,respectively,when the depth increased from 200-300 m to 1 100-1 200 m. This study demonstrates that middeep carbonate reservoirs possess an enhanced CO₂ dissolutionmineralization storage capacity under increasing pressure,providing experimental support for various karstrelated carbon sinks,particularly for CO₂ sequestration in depleted carbonate oil and gas reservoirs.