## 3 Results and Discussion
### Effects of CO\({}_{2}\) Injection Rate  
The dynamic responses of pore volume and reservoir pressure to varying CO\({}_{2}\) injection rates in limestone and dolostone reservoirs are demonstrated in Figures 7 and 8. Specifically, Figure 7 delineates the increment in pore volume and the corresponding reservoir pressure build-up in the limestone reservoir during CO\({}_{2}\) injection at injection rates of 0.1, 0.5, and 1 mol/min. Figure 8 illustrates the same results, but in the dolostone reservoir. Figure 7: The comparison of (**a**) pore volume (PV) increase and (**b**) pressure increment in the limestone reservoirs during CO\({}_{2}\) injection with different injection rates of 0.1, 0.5, and 1.0 mol/min. It is observed that the pore volume expansion within both limestone and dolostone reservoirs inversely correlates with the CO2 injection rate. For instance, the pore volumes increase by 8.5% and 0.16% in the respective limestone and dolostone reservoirs at a CO2 injection rate of 0.1 mol/min. In contrast, the increases in pore volume in the limestone and dolostone reservoirs are merely 0.85% and 0.016%, respectively, at a higher injection rate of 1 mol/min, which are ten times less than those at the lower injection rate of 0.1 mol/min. The mechanism for this inverse relationship is attributed to the slower injection rates, which provide a longer residence time for CO2 to physically dissolve and chemically interact with the carbonate rock matrix, thereby facilitating a greater increase in pore volume. It is worth noting that the reduction in pore volume increase is not linearly proportional to the increase in CO2 injection rate. For instance, in the limestone reservoir, a five-fold increase in the CO2 injection rate from 0.1 mol/min to 0.5 mol/min can result in an 8.5-fold reduction in pore volume increase. However, doubling the injection rate further to 1 mol/min only led  
Figure 8: The comparison of (**a**) pore volume (PV) increase and (**b**) pressure increment in the dolostone reservoirs during CO2 injection with different injection rates of 0.1, 0.5, and 1.0 mol/min. to a 1.6-fold reduction in the pore volume increase. This phenomenon illustrates the non-linear and more pronounced impact of CO2 injection rates at lower ranges on pore volume expansion. Conversely, reservoir pressure exhibits a directly proportional relationship with the CO2 injection rates, which is opposed to the trend observed in pore volume changes. This observation is consistent with the established understanding that an inverse relationship exists between pore volume and reservoir pressure; a faster rate of pore volume increase leads to a comparatively slower rate of reservoir pressure buildup. The findings suggest the existence of an optimal CO2 injection rate for carbonate reservoirs. While a rapid injection rate may expedite reaching CO2 storage targets and reduce costs, it could potentially compromise the long-term maximum CO2 storage capacity of the reservoirs, indicating a trade-off between immediate efficiency and future storage potential. Overall, the findings challenge traditional perceptions regarding carbonate reservoir suitability for CO2 storage, particularly highlighting the favorable characteristics of pore-dominant limestone reservoirs with small pore sizes, which is very much against the traditional opinion of seeking high-permeable fracture-dominant dolostone reservoirs with large pore sizes. This underscores the importance of constantly reevaluating reservoir characteristics because of CO2 injection-induced modifications. It is also worth noting that this study aims to investigate the effects of CO2-brine-carbonate rock interactions from a mechanistic perspective. Thus, the geological model was ideally constructed, such as the geological features of homogeneity, pore space of perfect spherical and cylindrical shape, uniform pore size, etc. It is evident that the actual carbonate reservoirs are far more complex than the geological model constructed in this paper.