Experimental Study on the Density-Driven Convective Mixing of CO 2 and Brine at Reservoir Temperature and Pressure Conditions

The reduction in CO 2 emissions from fossil fuel combustion represents a major challenge worldwide. Carbon capture and storage technology is an important approach to reducing CO 2 emissions. Convective mixing is an important storage mechanism that enhanced dissolution of CO 2 with safe and high efficiency during CO 2 storage in saline aquifers. In this study, a series of convective mixing experiments between CO 2 and saline were conducted at reservoir temperature and pressure using a high-pressure Hele-Shaw cell. The onset and development of the finger during convective mixing were visually observed. The onset time of the finger was 20 s, and the whole convective mixing process took approximately 240 s. Moreover, the absorbance of the solution was measured, and then the ionization of CO 2 solution and concentration of dissolved CO 2 were successfully connected under various pressures and salinities. The CO 2 dissolution rate of the case of 38 °C, 10 g/L, and 11 MPa ranged from approximately 3.84 to 5.259 mmol L –1 s –1, which was 1.135–3.514 mmol L –1 s –1 faster than that of other conditions. It was shown that higher pressure promotes the formation and development of the finger to improve the average dissolved CO 2 concentration and CO 2 dissolution rate. However, higher salinity has the opposite effect. The case of 38 °C, 10 g/L, and 11 MPa has the best promoting effect on the mass transfer of convective mixing. Therefore, the condition of high pressure and low salinity is beneficial for convective mixing.