The objective of this work is to investigate fluid-rock reactions in Mt. Simon sandstone to shed light on micro-seismicity during carbon dioxide geological sequestration. We studied the influence of incubation in high relative humidity (85%) on the elasticity, strength and fracture behavior of Mt. Simon sandstone specimens using a combination of scratch tests, nano-indentation tests, along with advanced imaging techniques such as high-resolution scanning electron microscopy and atomic force microscopy (AFM). Scanning electron microscopy reveals a granular microstructure mainly composed of K-feldspar and quartz grains intermixed with micropores. Meanwhile, at the nanoscale, nanoporous clay exist at the interface between grains. In this study, we investigated the water-rock reactions using microscopic scratch testing combined with statistical nanoindentation. The fracture toughness is evaluated using microscopic scratch tests and nonlinear fracture mechanics. On the other hand, statistical indentation is utilized to measure porosity changes in various specimens. A decrease in fracture toughness is observed after just 48 hours of incubation at high relative humidity (85%). AFM reveals an increase in surface roughness consistent with secondary precipitation reactions. Furthermore, scanning electron microscopy reveals the presence of mineral precipitation at grain boundaries. The results presented are important to understand the impact of geochemical reaction on the mechanical properties of the host rock.

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