Experimental Studies On CO₂（SO₂）-saline-minerals Interaction Under Geological Storage Condition

At present, geologic CO2 sequestration(GCS) in deep saline aquifers is the most effective way to reduce CO2 emissions. CO2, as a weak acid gas, would interact with the reservoir minerals during and after injection, this may change the porosity and permeability of formation rocks. However, the injected CO2 is not pure, always containing several reducing gases. With a high solubility into water than CO2, SO2 can form sulfuric acid after dissolving, which might seriously reduce the p H value of the solution and accelerate the water-rock reaction. The focus of this experiment is to investigate the impure gas-brine-minerals interactions after CO2 injection.In this work, pure CO2 and impure CO2(Vol. %CO2: Vol.%SO2=99.5%/: 0.5%) were reacted with calcite and feldspar(as the representatives of carbonate and silicate minerals respectively) for different time. Cleaved surfaces of minerals were exposed to the Scanning Electron Microscope(SEM) and the solutions were tested by Inductively Coupled Plasma Optical Emission Spectroscopy(ICP-OES), it can provide information for the actual sequestration.SEM results showed the dissolution of the calcite surface after reacted with both pure and impure CO2, but the corrosion pits is deeper in the mixed system. A few of corrosion pits and secondary minerals were showed on the feldspar surface after reactions in two systems. The platy secondary minerals generated near the corrosion pits piled up into rose-like shape on early formed flakes after reaction with pure CO2. While in the mix system, the secondary minerals grew preferentially on feldspar surface and developed into a thin layer. According to the results of the Energy Dispersive Spectrometer(EDS), the secondary minerals were confirmed to be kaolinite and some phyllosilicate. The results of ICP-OES indicated SO2 only exacerbated the dissolution of calcite and changed the development area of secondary minerals on feldspar surface.