Importance of diagenetic heterogeneity in Chang 7 sandstones for modeling CO2-water-rock interactions

The diagenetic heterogeneity of the tight sandstone of Yanchang Formation in Ordos Basin is significant, and the surface area of reactive minerals varies greatly among different types of sandstones. Geochemical modeling was used to assess the impact of diagenetic heterogeneity on CO2-water-rock interactions in Chang 7 sandstones. Reactive surface area (RSA) for each mineral was determined using image analysis and the results were inte-grated into geochemical simulations of CO2-water-rock interactions to assess the mineralogical evolution of different diagenetic facies sandstones after CO2 injection. The simulation results show that the mineralogical evolution and porosity change of sandstones with different diagenetic facies are different under the same CO2- rich fluid environment, and the mineralization amount is also different. The results of this study show that even under similar sedimentary environment, tectonic location and burial-thermal history conditions, the differential response of different diagenetic facies to CO2-rich fluids cannot be ignored. It is necessary to consider the effect of diagenetic heterogeneity when evaluating CO2 sequestration at large scale.