The interfacial properties of clay-coated quartz at reservoir conditions
School of Engineering
Funding information available at: https://doi.org/10.1016/j.fuel.2019.116461
Shale interfacial properties are important for CO2 geo-sequestration and CH4 recovery in shale formation. In this work we use a newly-developed and well-defined shale model (i.e. a clay-coated quartz) to systematically evaluate the influence of kaolinite and montmorillonite, as primary constituents of shales, on CO2 shale-wettability, and shale-CO2, shale-CH4, and shale-water surface energies. Specifically, we measure CO2 wettability of clay-coated quartz and the related CO2-brine and CH4–brine interfacial tensions at various pressures and temperatures. We calculate the surface free energies of the clay-coated quartz versus CO2 and CH4 using Neumann's equation. The results demonstrate that clay coating leads to a less hydrophilic surface at a low temperature (i.e. 300 K), while it renders the surface more hydrophilic at a high temperature (i.e. 353 K); however, clay coating has only a small influence on the quartz-CO2 and quartz-CH4 surface energies. In addition, higher CO2 pressures always result in less water-wet surfaces for clean, kaolinite-coated and montmorillonite-coated quartz samples at the temperatures tested (i.e. 300 K and 353 K). Moreover, higher CO2 and CH4 pressures lead to smaller mineral-CO2 and mineral-CH4 surface energies, respectively. An increase in temperature shows a complicated effect, i.e. it increases the surface energies of mineral-CO2 while it reduces those of mineral-CH4 (slightly) and clay-coated quartz-brine systems. For similar pressure and temperature values, the surface energies of mineral-CO2 system are always smaller than those of the corresponding mineral-CH4 systems. The results can aid the predictions of CO2 storage capacity, leakage risk assessments, and CH4 recovery.