文摘
Geologic storage of CO<sub>2sub> requires that the caprock sealing the storage rock is highly impermeable to CO<sub>2sub>. Swelling clays, which are important components of caprocks, may interact with CO<sub>2sub> leading to volume change and potentially impacting the seal quality. The interactions of supercritical (sc) CO<sub>2sub> with Na saturated montmorillonite clay containing a subsingle layer of water in the interlayer region have been studied by sorption and neutron diffraction techniques. The excess sorption isotherms show maxima at bulk CO<sub>2sub> densities of 鈮?.15 g/cm<sup>3sup>, followed by an approximately linear decrease of excess sorption to zero and negative values with increasing CO<sub>2sub> bulk density. Neutron diffraction experiments on the same clay sample measured interlayer spacing and composition. The results show that limited amounts of CO<sub>2sub> are sorbed into the interlayer region, leading to depression of the interlayer peak intensity and an increase of the d(001) spacing by ca. 0.5 脜. The density of CO<sub>2sub> in the clay pores is relatively stable over a wide range of CO<sub>2sub> pressures at a given temperature, indicating the formation of a clay-CO<sub>2sub> phase. At the excess sorption maximum, increasing CO<sub>2sub> sorption with decreasing temperature is observed while the high-pressure sorption properties exhibit weak temperature dependence.