In Situ Study of CO2 and H2O Partitioning between Na鈥揗ontmorillonite and Variably Wet Supercritical Carbon Dioxide

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• 作者：John S. Loring ; Eugene S. Ilton ; Jeffrey Chen ; Christopher J. Thompson ; Paul F. Martin ; Pascale B茅n茅zeth ; Kevin M. Rosso ; Andrew R. Felmy ; Herbert T. Schaef
• 刊名：Langmuir
• 出版年：2014
• 出版时间：June 3, 2014
• 年：2014
• 卷：30
• 期：21
• 页码：6120-6128
• 全文大小：371K
• 年卷期：v.30,no.21(June 3, 2014)
• ISSN：1520-5827

文摘

Shale formations play fundamental roles in large-scale geologic carbon sequestration (GCS) aimed primarily to mitigate climate change and in smaller-scale GCS targeted mainly for CO₂-enhanced gas recovery operations. Reactive components of shales include expandable clays, such as montmorillonites and mixed-layer illite/smectite clays. In this study, in situ X-ray diffraction (XRD) and in situ infrared (IR) spectroscopy were used to investigate the swelling/shrinkage and H₂O/CO₂ sorption of Na⁺-exchanged montmorillonite, Na-SWy-2, as the clay is exposed to variably hydrated supercritical CO₂ (scCO₂) at 50 掳C and 90 bar. Measured d₀₀₁ values increased in stepwise fashion and sorbed H₂O concentrations increased continuously with increasing percent H₂O saturation in scCO₂, closely following previously reported values measured in air at ambient pressure over a range of relative humidities. IR spectra show H₂O and CO₂ intercalation, and variations in peak shapes and positions suggest multiple sorbed types of H₂O and CO₂ with distinct chemical environments. Based on the absorbance of the asymmetric CO stretching band of the CO₂ associated with the Na-SWy-2, the sorbed CO₂ concentration increases dramatically at sorbed H₂O concentrations from 0 to 4 mmol/g. Sorbed CO₂ then sharply decreases as sorbed H₂O increases from 4 to 10 mmol/g. With even higher sorbed H₂O concentrations as saturation of H₂O in scCO₂ was approached, the concentration of sorbed CO₂ decreased asymptotically. Two models, one involving space filling and the other a heterogeneous distribution of integral hydration states, are discussed as possible mechanisms for H₂O and CO₂ intercalations in montmorillonite. The swelling/shrinkage of montmorillonite could affect solid volume, porosity, and permeability of shales. Consequently, the results may aid predictions of shale caprock integrity in large-scale GCS as well as methane transmissivity in enhanced gas recovery operations.