Effect of supercritical CO2 treatment on physical properties and functional groups of shales

The influence of Supercritical CO2 (SCCO2) on geochemical interaction is considered a key factor affecting CO2 storage capacity in shales. To address this issue, samples from Eagle Ford and Mancos shales were treated with SCCO2 for 30 days at 70 degrees C and 18 MPa. Analytical methods including X-ray diffraction (XRD), optical microscope, and Fourier Transform Infrared spectroscopy (FTIR) were used. The alteration in shale/water contact angles was evaluated based on Sessile drop method. The results show that SCCO2 treatment can alter the mineral composition of shales. Quartz content generally increased, while clay and carbonate minerals' contents decreased. Evaluating the dissolution of carbonate minerals, in particular, is beneficial to form an effective mineral carbonation trapping for long-term CO2 storage. The changes in surface morphology suggest that clay rich shales are more affected by SCCO2 treatment compared to sandy/quartz-rich shales. The aromatic hydrocarbons showed minor changes after SCCO2 treatment compared to the aliphatic hydrocarbons. The increase in oxygen-containing groups after SCCO2 treatment proves the high adsorption capacity of CO2 in shales. However, hydroxyl functional groups showed various trends after SCCO2 treatment, depending on the clay content. Eagle Ford shales displayed a possible turn to CO2-wet behavior, while the surface of Mancos shales remained strongly hydrophilic. In conclusion, quartz-rich shales could be favorable for CO2 adsorption and providing more storage capacity.

Automated summary

The treatment of shales with supercritical CO2 can alter mineral composition, with an increase in quartz content and decrease in clay and carbonate minerals, providing benefits for long-term CO2 storage. Shales rich in clay are more susceptible to SCCO2 treatment, and the increase in oxygen-containing groups indicates a high adsorption capacity for CO2. The behavior of functional groups post-SCCO2 treatment varies depending on clay content, and quartz-rich shales may be more favorable for CO2 adsorption and storage capacity.