In situ XRD study of Ca²⁺ saturated montmorillonite (STX-1) exposed to anhydrous and wet supercritical carbon dioxide

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• 作者：H.T. Schaef ; ^{todd.schaef@pnl.gov} ; E.S. Ilton ; O. Qafoku ; P.F. Martin ; A.R. Felmy ; K.M. Rosso
• 关键词：Carbon sequestration ; Caprock ; Montmorillonites ; In situ XRD
• 刊名：International Journal of Greenhouse Gas Control
• 出版年：2012
• 出版时间：January 2012
• 年：2012
• 卷：6
• 期：Complete
• 页码：220-229
• 全文大小：1389 K

文摘

Reactions involving supercritical carbon dioxide (scCO₂) and a calcium saturated dioctahedral smectite (Ca-STX-1) were examined by in situ high-pressure X-ray diffraction over a range of temperatures (50-100 ¡ãC) and pressures (90, 125, and 180 bar) relevant to long-term geologic storage of CO₂. Exposure of Ca-STX-1 containing one water of hydration (1 W) to anhydrous scCO₂ at 50 ¡ãC and 90 bar produced an immediate increase of ?.8 ? in the d_0 0 1 basal reflection that was sustained for the length of the experiment (?4 h). Higher ordered basal reflections displayed similar shifts. Following depressurization, positions of basal reflections and FWHM values (d_0 0 1) returned to initial values, with no measurable modification to the clay structure or water content. Similar results were obtained for tests conducted at 50 ¡ãC and higher pressures (125 and 180 bar). Exposure of Ca-STX-1 containing two waters of hydration (2 W) to scCO₂ resulted in a decrease in the d_0 0 1 reflection from 14.48 ? to 12.52 ?, after pressurization, indicating a partial loss of interlayer water. In addition, the hydration state of the clay became more homogeneous during contact with anhydrous scCO₂ and after depressurization. In the presence of scCO₂ and water, the clay achieved a 3 W hydration state, based on a d_0 0 1 spacing of 18.8 ?. In contrast to scCO₂, comparable testing with N₂ gas indicated trivial changes in the d_0 0 1 series regardless of hydration state (1 W or 2 W). In the presence of free water and N₂, the basal spacing for the Ca-STX-1 expanded slightly, but remained in the 2 W hydration state. The experiments show that potential collapse or expansion of the interlayer spacing depends on the initial hydration state of the clay and scCO₂, where 1 W clay is stable but ? W layer clay loses water when exposed to anhydrous CO₂. Consequently, the implications of this study depend upon the depth of the caprock. If the caprock is quite deep, then the 1 W hydration state is favored and the introduction of dry CO₂ could actually help seal the formation. If the caprock is located closer to the surface where 2 W or 3 W montmorillonite is the predominant form then the introduction of dry CO₂ should result in the creation of permeability. Further, these experiments indicate that scCO₂ can become intercalated within hydrated clays under conditions proposed for geologic storage of CO₂ and act as secondary CO₂ traps.