Fundamental study of CO2-H2O-mineral interactions for carbon sequestration, with emphasis on the nature of the supercritical fluid-mineral interface.

Abstract

In the supercritical CO 2 -water-mineral systems relevant to subsurface CO 2 sequestration, interfacial processes at the supercritical fluid-mineral interface will strongly affect core-and reservoir-scale hydrologic properties. Experimental and theoretical studies have shown that water films will form on mineral surfaces in supercritical CO 2 , but will be thinner than those that form in vadose zone environments at any given matric potential. The theoretical model presented here allows assessment of water saturation as a function of matric potential, a critical step for evaluating relative permeabilities the CO 2 sequestration environment. The experimental water adsorption studies, using Quartz Crystal Microbalance and Fourier Transform Infrared Spectroscopy methods, confirm the major conclusions of the adsorption/condensation model. Additional data provided by the FTIR study is that CO 2 intercalation into clays, if it occurs, does not involve carbonate or bicarbonate formation, or significant restriction of CO 2 mobility.We have shown that the water film that forms in supercritical CO 2 is reactive with common rock-forming minerals, including albite, orthoclase, labradorite, and muscovite. The experimental data indicate that reactivity is a function of water film thickness; at an activity of water of 0.9, the greatest extent of reaction in scCO 2 occurred in areas (step edges, surface pits) where capillary condensation thickened the water films. This suggests that dissolution/precipitation reactions may occur preferentially in small pores and pore throats, where it may have a disproportionately large effect on rock hydrologic properties.Finally, a theoretical model is presented here that describes the formation and movement of CO 2 ganglia in porous media, allowing assessment of the effect of pore size and structural heterogeneity on capillary trapping efficiency. The model results also suggest possible engineering approaches for optimizing trapping capacity and for monitoring ganglion formation in the subsurface. 6 ACKNOWLEDGMENTS

Impact of Exposure to Supercritical Carbon Dioxide on Reservoir Caprocks and Inter-Layers during Sequestration

“…An investigation by Shao et al [40] focused on phlogopite and showed no carbonation following treatment with water-saturated scCO 2 at 103 bar and 95 • C for 159 h. Dissolution pits, and secondary precipitation of silica and kaolinite were observed, however. These results were in agreement with an experiment on muscovite conducted by Bryan et al [41], who observed the same dissolution pits and secondary precipitation after a 14 day treatment in water-saturated scCO 2 at 50 • C and 138 bar. Again, carbonation was not observed.…”

“…Wet CO 2 treatment (14 days at 50 • C and 138 bar) experiments on albite conducted by Bryan et al [41] showed dissolution features and the suspected precipitation of silica and phyllosilicates. A similar result was seen by Regnault et al [45] when investigating another plagioclase feldspar, anorthite.…”

Critical Knowledge Gaps for Understanding Water–Rock–Working Phase Interactions for Compressed Energy Storage in Porous Formations

“…This can result in the precipitation of salt crystals in the formation ,− or in caprock fractures, blocking or reducing flow pathways . Residual water films may form on grain surfaces in the CO 2 -saturated region in water-wet formations . Experimental work has shown that these water films are reactive, resulting in mineral dissolution and precipitation reactions where these reactions may preferentially occur in small pores and pore-throats where water films dominate …”