Investigating the Mineralogical and Chemical Effects of CO₂ Injection on Shale Wettability at Different Reservoir Temperatures and Pressures

Abstract

The wettability of shale, which determines the success of carbon dioxide-enhanced shale gas recovery (CO 2 -ESGR) and the safety of CO 2 geo-storage, is influenced due to shale−CO 2 chemical interactions. To date, the wettability alteration mechanism of shale by its surficial chemical groups is not well understood. In this study, the variations in the wettability, mineralogy, and infrared spectrum of shale after interaction with CO 2 at different temperatures and pressures were studied using the sessile drop method, X-ray diffraction, and Fourier transform infrared spectroscopy analysis. The effect of the contents of minerals and chemical groups on shale wettability was investigated by correlation analysis. It is found that the pressure of CO 2 has a larger influence on shale wettability than the temperature, whereas the temperature has a greater effect on the infrared spectra of shale. Quartz has the greatest effect on wettability followed by carbonate and clay minerals. Quartz is originally water-wet, and the negative correlation between the relative quartz content and the wettability of shale implies the deterioration of the quartz hydrophilicity after CO 2 treatment, and the same applies to the oxygen-containing groups. These findings indicate the interactions among functional groups and their redistribution on the surface during shale−CO 2 interactions. Si−O groups are derived more from the hydrophobic Si−O−Si groups than hydrophilic Si−OH groups after CO 2 treatment, reducing the contribution of quartz to shale hydrophilicity. The weakened absorption ability of CO 3 2− ions to water may be caused by the rotation and redistribution of the CO 3 2− groups on the surface after the CO 2 treatment. A longer aliphatic hydrocarbon length reduces the shale wettability. Among the hydrophilic −OH groups, free −OH has the largest influence on shale wettability followed by −OH−O, −OH−OH, and −OH−Π. This study has important theoretical significance for understanding the wettability alteration mechanism of shale.

Impact of Supercritical CO2 on Shale Reservoirs and Its Implication for CO2 Sequestration

“…However, if the organic matters present in the shales are in thin laminations, then the percolation threshold would be higher across lamination and lower in the direction perpendicular to it. − Therefore, it suggests that even if the percolation threshold is below or above 12%, the alteration in shale wettability would also be dependent on the direction of organic matter laminations, with respect to the direction of the upward-moving CO 2 . Similarly, the presence and distribution of functional groups within shale surfaces have been observed to strongly influence the shale wettability behavior . Future studies should evaluate these aspects.…”

“…Similarly, the presence and distribution of functional groups within shale surfaces have been observed to strongly influence the shale wettability behavior. 236 Future studies should evaluate these aspects. In a summary, the key parameters that affect the wettability of the shales are pressure, temperature, TOC, mineralogical composition, organic matter connectivity (percolation threshold), distribution, fluid properties, and surface chemistry.…”

Wettability and Its Influencing Factors of Tight Sandstones in Coal Measures in Ordos Basin, China

“…Although they are all water-wet minerals, pyrite, carbonate, and clay minerals negatively affect sandstone hydrophilicity, while quartz has a positive effect, and this was confirmed by other work. 35 − 37 Based on our 29 samples, the range and average content of each mineral for these three types of sandstones are listed in Table 3 .…”

Comprehensive Review of Property Alterations Induced by CO2–Shale Interaction: Implications for CO2 Sequestration in Shale

“…The wettability of shale plays a crucial role in controlling adsorption, diffusion, and flow behaviors, which significantly affect CO 2 storage capacity and containment security. − The wettability of shale has a significant influence on the CO 2 injectivity, transport, and sweep efficiency in shale formation, which influences the ultimate CO 2 storage efficiency of the shale formation. In addition, potential leakage ways of CO 2 in caprock include diffusion, fracture flow, and capillary breakthrough, which are also significantly influenced by the wettability behavior of the shale. − …”