Study of Density Driven Convection in a Hele-Shaw Cell with Application to the Carbon Sequestration in Aquifers

Abstract

Faster dissolution of CO2 within aquifers plays a crucial role in the optimal storage of carbon dioxide injected into reservoirs. The mixture of CO2 and brine triggers convection currents in the aquifer and creates a remarkable increase of the dissolution rate of carbon dioxide. It is very vital for the risk assessment of leakage to obtain accurate description of the CO2 dissolution rate in the aquifers. In our experiments a series of CO2 solute-driven convection laboratory tests were performed in transparent vertical Hele-Shaw cells with a 1.2 mm gap that contained brine water overlain by gas phase and visualization of convective phenomena was achieved with the help of bromocresol purple completely solved into the brine at first. After CO2-brine film come to existence, small phase fingers caused by density contrast would form and they merge, widen, and penetrate deep into the cell. Much series of images recording the dynamic convection were analyzed. Binarization process can help calculate timescale changes of average/all rich- CO2-area which present mass transfer rate of CO2 into the brine. Effects of such different formation parameters as brine concentration, temperature, high pressure and heterogeneity on the onset and development of convection are investigated in our study. Two time intervals, including onset time and developing time took our most attention. Increasing system Rayleigh number, the formation parameters can greatly strengthen the convective mixing and accelerate the growth of CO2 solution into the test cell. The sodium chloride solution concentration gradient has an obvious influence on the form and development of convection phenomenon in our experiments. Here, only part results are exhibited in this paper and much further work are under way.