Influence of CO2 with impurities on dissolution law of sandstone

The CO2 captured from the flue gas of coal-fired power plants usually contains other gases such as nitrogen oxides， sulfur oxides， and O2. These gases may threaten safe CO2 sequestration after they are injected with CO2 into formation. However， there are still some gaps in Chinese and overseas research on the influence of CO2 with impurities on the dissolution law of sandstone. Therefore， this paper took a sandstone reservoir in an oilfield as the research object and conducted an experimental study on the reaction of CO2 containing different concentrations of NO2， SO2， and NO2 + SO2 with formation water and reservoir rock under different reaction times， temperatures， and pressures. Atmospheric-pressure and high-pressure tests were carried out， respectively. The dissolution rate， micro-morphology， composition， and mechanical properties of the core before and after the reaction， as well as the cation concentration in the solution after the reaction， were analyzed. The results show that during the reaction among other gas， CO2， formation water， and reservoir rock， feldspar， dolomite， chlorite， and other minerals in the core are dissolved， and core dissolution mainly occurs in feldspar； quartz is slightly dissolved when the reaction time reaches 21 days. The core dissolution rate increases as the reaction time increases. The core dissolution rate also increases when the pressure changes from atmospheric pressure to 10 MPa， indicating that the reaction time and pressure have a noteworthy influence on the core dissolution rate. For the same impurity concentration， SO2 is more likely to dissolve sandstone than NO2， and the core dissolution rate is higher when SO2 and NO2 are injected simultaneously. The injection of NO2 decreases the tensile strength and Poisson’s ratio of sandstone and increases the elastic modulus. The SO2 injection increases the tensile strength and elastic modulus of the core and decreases the Poisson’s ratio of the core.