Supercritical CO2 Storage in Shale Reservoirs: Implications of the Clay Mineral Interactions
Authors:   Intertek Westport Technology Center, Palencia Clara , Shehata Ahmed ,   Intertek Westport Technology Center, Harrell Benjamin ,   Intertek Westport Technology Center, Funk James ,   University of Houston, Hathon Lori ,   University of Houston, Myers Michael ,   University of Houston
Published: November 2024

Solar and wind power generation technologies currently do not exist to replace fossil fuels; therefore, long-term underground CO2 storage is the only practical solution for heavy industries to keep providing energy to the world and simultaneously meet their net-zero commitments by 2040. Geological sequestration (GS) includes depleted oil and gas reservoirs, coalbed methane, shale gas reservoirs, and aquifers. Aquifers have the greatest potential because of their relative abundance, but shale reservoirs are attractive in terms of areal extension, multiple porosity systems, and CO2 adsorption to shale, which increases their overall storage capability. Unfortunately, there is still a general lack of understanding of CO2-water-mineralogy interaction, particularly at high-temperature/high-pressure (HTHP) conditions. Additionally, there are inconsistencies among the existing data published in the literature. Static rock-fluid interaction experiments and high-frequency nuclear magnetic resonance (NMR) core measurements were acquired to evaluate the impact of mineralogy, clay mineral volume, and speciation on the total space available for storage. Three different core samples from shale reservoirs were used in the study, a terrigenous argillaceous (Haynesville Formation), a carbonaceous argillaceous (Eagle Ford), and a siliceous argillaceous sample (Barnett), with the idea of evaluating what kind of shale reservoir is more suitable to store CO2. In addition, nanopore gas adsorption and mercury injection capillary pressure (MICP) were combined to analyze the full pore spectrum of three different shale gas reservoirs. High-frequency NMR (24 MHz) T2 distribution and T1T2 maps were acquired in as-received, water-saturated, and post-supercritical CO2-water-rock exposure to evaluate the evolution of the bound water and the porosity systems. Preliminary results suggest that the bound- and free-water peak position of T2 distribution spectra of the post-CO2 injection shifted to the left, indicating an interaction between the CO2 and both waters that are making hydrogens atoms decay faster. The shift is clay mineral type dependence. From the preliminary results, it is observed that the CO2 adsorption capacity differs significantly from one shale play to the other, indicating an average of 5 to 10% gain in total porosity when compared to MICP data alone. In the carbonaceous argillaceous mudrock sample, reactions with CO2 created precipitates, heterogeneities, and unstable conditions for CO2 storage. The same analysis was performed in cuttings in other to compare results. These results will not only increase the understanding of CO2 in clay-bound water systems promoting safety and potential CO2 storage in clayey sediments but also broaden the knowledge of the positive and negative effects of different shale mineralogy as potential sites for CO2 storage. This research is an early step to evaluate the impact of maturity, clay content, and microscale and nanoscale fabrics on CO2 storage or utilization as an enhanced oil recovery (EOR).