In-situ 3D porosity-mineral comparison model has been established in the paper. Minerals such as potassium (K) feldspar, albite, NaCl and calcite are variably dissolved after the experiments. The dissolution, migration and reprecipitation of clay minerals are common, which is characterized by chlorite dissolution and the destruction of the original growth framework. Preliminary statistics show that the porosity and permeability of Chang 7 tight sandstones decreased by 60~80% after the experiment. The permeability reduction is positively related to the clay mineral content. It is the precipitation and re-migration of clay particles (e.g., kaolinites and smectites) released by the dissolution, which have been transported in the fluid flow path and accumulated at pore throats, that result in the changes of the pore system and the decrease of physical properties. The results provide new insights into CO2 trapping mechanisms in tight oil reservoirs, and into the potential formation damage that may result from massive injections of CO2 into reservoirs during EOR and CCUS programs.


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