Chemo-mechanical Alteration of Silicate-Rich Shale Rock after Exposure to CO2-Rich Brine at High Temperature and Pressure

• Published in: Rock mechanics and rock engineering 2024-08, Vol.57 (8), p.5317-5333
• Main Authors: Prakash, Ravi, Mahgoub, Samah A., Abedi, Sara
• Format: Article
• Language: English
• Subjects: Brines; Carbon dioxide; Carbon sequestration; Chemical precipitation; Civil Engineering; Clay; Computed tomography; Depth; Dissolution; Dissolving; Distance; Earth and Environmental Science; Earth Sciences; Enhanced geothermal systems; Enhanced oil recovery; Feldspars; Geophysics/Geodesy; High temperature; Image analysis; Image processing; Indentation; Ionic strength; Mechanical analysis; Mechanical loading; Mechanical properties; Microcracks; Oil recovery; Original Paper; Permian; Phases; Photosystem I; Porosity; Precipitation; Quartz; Rock properties; Rocks; Sediment samples; Sedimentary rocks; Shale; Shales; Silicates; Sodium chloride; Solubility
• ISSN: 0723-2632; 1434-453X
• DOI: 10.1007/s00603-023-03664-x

Owing to their application in rock weathering concerning geostructural stability, enhanced geothermal systems, carbon sequestration, and enhanced oil recovery, the effect of rock–brine–CO 2 interactions on the microstructural and mechanical properties of rocks has become a prevalent topic. Understanding the interplay among chemical, microstructural, and mechanical processes is essential to comprehend how they affect rock mechanical alteration. In this study, we examined the effects of chemo-mechanical loading on the microstructural features and mechanical alterations of individual components within the rock. Experiments involved exposing the Permian rock samples to either CO 2 or N 2 -rich brine (a control condition) at a temperature and pressure of 100 °C and 1800 Psi, respectively, for varying duration (14 and 28 days). The ionic strength of the solution was adjusted to 1 M using NaCl. Micro-CT image analysis showed the dissolution of clay- and quartz-rich phases followed by their precipitation. After 14 days, the depth of the outer reacted zone reached roughly 1100 µm, and after 28 days, the depth increased to 1500 µm. Microscale mechanical analysis showed decreased indentation modulus of the clay- and quartz-rich phases after reacting with CO 2 -rich brine. This decrease in indentation modulus was more than 50% for quartz-rich phases for 28 days of reaction and was lower adjacent to the reacted surface. The decrease in mechanical properties was more pronounced at a distance of 400–600 µm from the reacted surface after 14 days of reaction with CO 2 -rich brine due to the pore-size controlled solubility phenomenon. Experiments conducted at a greater distance from the reacted surface (approximately 5 mm) revealed a weaker clay–quartz interface, possibly due to the formation of microcracks induced by the swelling of clay particles. Results for the N 2 condition show a superficial mechanical alteration of the rock constituents limited to a depth of 200 µm from the reacted surface. Highlights Study investigates chemo-mechanical and microstructural alteration of silicate-rich shale rock by CO 2 / N 2 -rich brines. Dissolution of clay and quartz-rich phases followed by the precipitation of clay and quartz from the transformation of feldspar grains in CO 2 condition. The modulus of clay- and quartz-rich zones decreased in reacted areas but increased near the surface in CO 2 samples. N 2 condition causes superficial mechanical alteration, minimal dissolution. Po