The CO2 dissolved in the aquifer will increase the density of brine, which can result in the instability of the gravity and prompt the onset of the viscous finger. The viscous finger will lead to the convective mix, accelerating the process of CO2 solution in the brine. However, the gas stream in the CO2 storage usually contains the impurities such as N2, O2, and SO2, which can change the density difference in the process of solution, and affect the solubility trapping in the CO2 sequestration.
In this paper, a numerical simulation method was used to study the effect of different impurities on the solubility trapping in the process of CO2 storage. Firstly, based on the PR-HV model, this paper calculated the solubility of CO2, N2, O2, and SO2 with different temperature and salinity and analysed the variation of the solubility. Then a multi-component numerical simulation model based on a certain aquifer layer was established to compare the CO2 dissolution rate and the onset time of the instability and analyze the influence of impurities in the CO2 stream on the solubility trapping. Finally, this paper clarified the impact on the CO2 storage and suggested that the concentration of the impurities should be controlled in a rational range for the perspective of the economy and efficiency.
The results show that the solubility of CO2 is higher than N2 and O2 in the saline water, and close to that of SO2. We applied the solubility data to the numerical simulation. The results of the numerical simulation shows that with the increase of the concentration of N2 or O2, CO2 dissolution rate has a decrease, and the onset time of the instability has an increase. It meas the longer time CO2 plume keeping in the state of good flowing capability and low density. The onset of viscous finger will be postponed, leading to a negative influence on the solubility trapping and the risk of the CO2 leak through fractures and faults. On the contrary, SO2 can shorten the onset time of the instability, which accelerates the viscous finger and prompts the solubility trapping. A further conclusion is that the effect of SO2 on the viscous fingering is more significantly than N2 and O2.
This paper deepens the understanding about the effect of the impure CO2 on the solubility trapping, and clarifies the effect of different impurities.