Zeta Potential of a Natural Clayey Sandstone Saturated With Carbonated NaCl Solutions at Supercritical CO 2 Conditions

• Published in: Geophysical research letters Vol. 49; no. 15
• Main Authors: Hidayat, Miftah, Sarmadivaleh, Mohammad, Derksen, Jos, Vega‐Maza, David, Iglauer, Stefan, Vinogradov, Jan
• Format: Journal Article
• Language: English
• Published: 16.08.2022
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL099277

Abstract The zeta potential is a measure of electric potential at the mineral‐electrolyte interfaces. The zeta potential of natural sandstones depends on mineralogy, electrolyte pH, concentration, composition, amount of dissolved CO 2 , and temperature. We report for the first time the zeta potential measured on clayey sandstone comprising quartz, kaolinite, illite, albite and microcline saturated with NaCl solutions at supercritical CO 2 conditions. Our results demonstrate that zeta potentials in clayey sandstone samples at supercritical CO 2 conditions are significantly different from similar measurements conducted under ambient conditions and from those obtained with clean sandstones. Supercritical CO 2 zeta potential remains negative but is influenced by clays and feldspars due to their significant presence and exposure to large pores, which yields less negative zeta potential compared to quartz, under identical conditions. Our results have significant implications to natural subsurface systems such as CO 2 geo‐sequestration sites, aquifers, geothermal sources and hydrocarbon reservoirs. Plain Language Summary Sandstone is a type of porous rock commonly found in natural subsurface settings. Generally, the main mineral found in sandstone is quartz. However, other minerals such as clays and feldspars are also often present in sandstones. When the formation water flows through porous sandstone, the rock surface becomes electrically charged as water contacts minerals of the rock. The property that describes electrical properties of rock‐water interface is termed the zeta potential, and it can be used to characterize subsurface flows and the wetting state of rocks. The zeta potential can be measured using the streaming potential method in the laboratory under conditions representative of subsurface systems. In this study we show that the zeta potential of clayey sandstone at supercritical CO 2 conditions is significantly different from the published data on clayey samples at ambient conditions and from clean sandstones comprising mostly quartz. Therefore, ignoring the effect of high content of dissolved CO 2 at high pressure and elevated temperature and the fact that other minerals in sandstone can modify the zeta potential might lead to misinterpretation of data and model estimates used a broad range of earth and environmental science applications. Key Points First measurements of zeta potentials in an intact clayey sandstone saturated with CO 2 ‐rich NaCl solutions at supercritical CO 2 conditions Zeta potential of clayey sandstone saturated with CO 2 ‐rich NaCl is less negative compared with NaCl equilibrated with atmospheric CO 2 The zeta potential of a clayey sandstone is more positive than that measured in a clean sandstone