Supercritical CO2 Dissolution and Mass Transfer in a Heterogeneous Pore Network
EMSL Project ID
49072
Abstract
At EMSL, a drainage experiment was conducted at 9 MPa and 40 degrees C by injecting supercritical CO2 (scCO2) into the sandstone-analogue pore network micromodel initially saturated by water free of dissolved CO2 (dsCO2). During the experiment, time-lapse images of dye intensity, reflecting dsCO2 concentration, were obtained. Through these images, we observed non-uniform dye intensities ranging from dsCO2-free to solubility levels in individual pores and pore clusters, with average intensity levels gradually increasing with time. The different rates of dissolution in different pores/clusters can be attributed to (1) fast scCO2 dissolution at scCO2-water interfaces, (2) rate-limited mass transfer due to limited interface areas, and (3) a transition from rate-limited to diffusion-limited mass transfer, revealed by detailed analysis on selected pores and pore clusters. The analysis also shows that two fundamental processes - CO2 dissolution at phase interfaces and diffusion of dsCO2 at the pore scale (10-100 micrometre) - are relatively fast. With an aim to quantitatively interpret the intensity data in terms of dsCO2 concentration, we first calibrated the dye using HCl to adjust pH over the range 3.7-6.5 (HCl was used due to the difficulty in measuring pH of CO2-bearing water), and from that we built the pH-intensity curve. However, by using this curve to interpret the dsCO2 concentration change within 4.5 hours, our observations indicate multiple orders of magnitude lower dsCO2 concentrations than the theoretical calculation. After obtaining more information on the dye from the manufacturer, we are now clear on the potential reason for this inconsistency. The pHrodo red AM dye, because it is uncharged, is not very soluble in aqueous solution. We suspect that there could be a difference in solubility between the HCl vs. CO2 calibration cases that is behind the differing intensity. Meanwhile, the dye is colorless and nonfluorescent until hydrolyzed. Differing AM hydrolysis would also explain the inconsistency. We think that additional experiments and treatments on the dye are crucial and particularly important to the study and complete the revision of the paper we submitted to Environmental Science & Technology. We aim to repeat our previous experiment with either a fully hydrolyzed AM dye or a fully soluble dye salt to obtain the needed quantification, with some additional experiments for addressing reviewers' concerns.
Project Details
Project type
Limited Scope
Start Date
2015-09-16
End Date
2015-11-16
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Chang C, Q Zhou, M Oostrom, T Kneafsey, and HS Mehta. 2017. "Pore-scale Supercritical CO2 Dissolution and Mass Transfer under Drainage Conditions." Advances in Water Resources 100:14-25. doi:10.1016/j.advwatres.2016.12.003
Chang C., Q. Zhou, T.J. Kneafsey, M. Oostrom, and Y. Ju. 2019. "Coupled supercritical CO2 dissolution and water flow in pore-scale micromodels." Advances in Water Resources 123. PNNL-SA-152825. doi:10.1016/j.advwatres.2018.11.004
Chang C, Q Zhou, TJ Kneafsey, M Oostrom, TW Wietsma, and Q Yu. 2016. "Pore-Scale Supercritical CO2 Dissolution and Mass Transfer under Imbibition Conditions." Advances in Water Resources 92:142-158. doi:10.1016/j.advwatres.2016.03.015
Chang C., T.J. Kneafsey, Q. Zhou, M. Oostrom, and Y. Ju. 2019. "Scaling the impacts of pore-scale characteristics on unstable supercritical CO2-water drainage using a complete capillary number." International Journal of Greenhouse Gas Control 86. PNNL-SA-152826. doi:10.1016/j.ijggc.2019.04.010