Effect of precipitation mineralization reactions on convective dissolution of ${\mathrm{CO}}_2$: An experimental study

To analyze the influence of a precipitation mineralization reaction between dissolved ${\mathrm{CO}}_2$ and calcium ions on the convective transfer of ${\mathrm{CO}}_2$ toward an aqueous phase, the convective dissolution of ${\mathrm{CO}}_2$ into aqueous solutions of calcium hydroxyde $\left[\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\right]$ and calcium chloride $\left({\mathrm{CaCl}}_2\right)$ of various concentrations is studied experimentally. We show that different precipitation patterns develop in the aqueous solution depending on the nature and concentration of the reactant in the host phase. In the case of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$, precipitation coupled to convection leads to vigorous convective mixing in the host phase and sedimentation of solid particles of calcium carbonate $\left({\mathrm{CaCO}}_3\right)$ down to the bulk of the reservoir. Conversely, dissolution of ${\mathrm{CO}}_2$ in buffered ${\mathrm{CaCl}}_2$ solutions leads to a stabilization of the buoyancy-driven convection due to a decrease in density and the adherence of the precipitate to the cell walls.

Figure 1

(a) Schematic of the experimental setup including Schlieren and direct visualization. (b) Design of the spacer and sketch of the two-layer stratification of ${\mathrm{CO}}_2$ and aqueous reactive solution in the Hele-Shaw cell. The red rectangle shows the zone followed in the study of the convective dynamics.

Figure 2

Schlieren images of the temporal development of the convective instability generated by the dissolution of gaseous ${\mathrm{CO}}_2$ in $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ solutions of increasing concentration from top to bottom at $t=150$, 300, 600, and 1800 s from left to right. The field of view is $8.8\times 5.5$ cm. An enlargement of the red rectangle of the image at $t=600$ s of the solution at $5\times {10}^{-3}\mathrm{M}$ is provided in Fig. 3.

Figure 3

Enlargement of the precipitation-driven convective pattern at $t=600$ s in a solution of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_{2}5\times {10}^{-3}\mathrm{M}$ (see red rectangle in Fig. 2). The main characteristics of the convective dynamics are highlighted: The gas-liquid interface where gaseous ${\mathrm{CO}}_2$ dissolves from above; the reaction front indicating the zone where the reaction rate is the largest; denser ${\mathrm{CO}}_2$ fingers just below the gas-liquid interface; ascending plumes, driven by an upward flow generated by chemical reactions and evacuated through rising small chimneys appearing at the upper limit of the reaction front; and precipitate fingers, containing solid ${\mathrm{CaCO}}_3$ particles sinking below the reaction front. The field of view is $4.0\times 1.5$ cm.

Figure 4

Direct view of the temporal development (from top to bottom) of precipitation-driven dynamics in $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ solutions in concentrations $5\times {10}^{-3}\mathrm{M}$ (left) and ${10}^{-2}\mathrm{M}$ (right). The field of view is $13.3\times 7.5$ cm.

Figure 5

Lines chosen to draw space-time maps: (1) 3 mm below the interface; (2) 1.3 mm above the reaction front; (3) position of the reaction front; (4) 1.3 mm below the reaction front; and (5) vertical line at the center of the image.

Figure 6

Space-time maps of the dynamics on a horizontal line 3 mm below the gas-liquid interface as a function of time in (a) water [7] and in $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ solutions of concentration (b) ${10}^{-4}$, (c) $5\times {10}^{-4}$, (d) ${10}^{-3}$, (e) $5\times {10}^{-3}$, and (f) ${10}^{-2}\mathrm{M}$. The horizontal length is 8.8 cm and the time resolution is 10 s. Time is running downward and the final time is 115 min.

Figure 7

Space-time maps of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_{2}5\times {10}^{-3}\mathrm{M}$ (a) above the reaction front and (b) below the reaction front. Space-time map of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2{10}^{-2}\mathrm{M}$ (c) above the reaction front and (d) below the reaction front. In each case, the horizontal length is 8.8 cm. Time is running downward up to 146 min.

Figure 8

Space-time maps of the dynamics along the vertical line at the center of pictures in solutions of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ (a) $5\times {10}^{-3}\mathrm{M}$ and (b) ${10}^{-2}\mathrm{M}$. Arrows indicate the location of some ascending plumes. Time is running horizontally, with a final time of 146 min. The vertical length is 5.5 cm.

Figure 9

Temporal evolution of the mixing length $L$ in water and in solutions of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ of various concentrations. Each curve represents the average on several experiments. The shaded zones around the curves represent the associated double standard deviation.

Figure 10

Averaged finger velocities as a function of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ concentration, computed from the slope of the temporal evolution of mixing lengths. Error bars represent the double of standard deviation.

Figure 11

Comparison of the Fourier spectra for solutions of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_{2}5\times {10}^{-4}$, ${10}^{-3}$, and $5\times {10}^{-3}\mathrm{M}$.

Figure 12

Visualization of pH changes in a solution of $\mathrm{Ca}{\left(\mathrm{OH}\right)}_{2}5\times {10}^{-3}\mathrm{M}$ by a universal color indicator at $t=5$ min (top) and $t=48$ min (bottom). The contrast and brightness of images have been modified to improve color contrasts, which explains the green area above the gas-liquid interface. The red circled area indicates a rising basic purple channel in the green intermediate area. The field of view is 16 cm wide.

Figure 13

Temporal development of the convective instability generated by the dissolution of ${\mathrm{CO}}_2$ in ${\mathrm{CaCl}}_2$ solutions of various concentration. The field of view is $8.8\times 5.5$ cm.

Figure 14

Direct view of precipitation pattern in solutions of ${\mathrm{CaCl}}_2$ (a) 0.01 and (b) 0.10 M after 2 h of experiment. The field of view is $13.5\times 6.6$ cm.

Figure 15

Space-time maps of the dynamics along a horizontal line 3 mm below the interface in solutions of borax alone (a) and of borax containing ${\mathrm{CaCl}}_2$ 0.01 (b), 0.05 (c), and 0.10 M (d). The width is 8.8 cm. Time is running downward with a maximum of 100 min.

Figure 16

Vertical space-time maps of the dynamics at the center of pictures in solutions of ${\mathrm{CaCl}}_2$ (a) 0.01; (b) 0.025; and (c) 0.10 M. The height is 5.5 cm. Time is running horizontally, and the maximum time is 100 min.

Figure 17

Comparison of the Fourier spectra for borax and varying ${\mathrm{CaCl}}_2$ concentrations (0, 0.01, and 0.10 M).

Figure 18

Comparison of the fingering pattern observed with the Schlieren technique at $t=10$ min in (a) water, (b) borax 0.0125 M, and (c) glycine 0.0125 M. The field of view is $8.8\times 5.5$ cm.

Figure 19

Comparison of the fingering pattern observed at $t=55$ min in glycine with ${\mathrm{CaCl}}_2$ 0.10 M (left) and 0.50 M (right). Black zones correspond to solid precipitate which has sedimented on the walls of the cell. The field of view is $8.8\times 5.5$ cm.

Figure 20

Comparison of convection in a solution of ${\mathrm{CaCl}}_2$ 0.10 M with a universal color indicator at $t=50$ min in borax 0.0125 M (left) and in glycine 0.0125 M (right). The field of view is 16 cm wide.