Characterization of the microstructural components and corrosion-induced changes in the mechanical properties of oolitic limestone

Abstract

The understanding of the variation of mechanical properties and microstructural changes of rocks due to chemical weathering is critical for prospection, extraction and storage of energy resources in the subsurface. Uniaxial and triaxial compression tests were conducted on fresh and chemically weathered oolitic limestone samples submerged in acidic solutions with pH5 and pH3 values for 30 and 50 days each. Results show that both, acid concentration and exposure period have a significant influence not only in changes of effective porosity, Young’s modulus and peak strength, but also in the development of stress-induced microstructures. While the change in effective porosity increased and the Young’s modulus decreased with exposure time, the peak strength decreased with exposure time and decreasing pH. Micro-fracturing, twinning, and rigid body rotation were the main mechanisms of the deformations observed. The highest density of microcracks and twinned grains were observed in samples subjected to longer exposure periods of time, suggesting that the exposure time constitutes an essential factor in rock softening. Microfracturing initiated at grain boundaries, where stress concentrations were higher. In agreement with previous work on limestone inelastic compaction, the mechanical contrast of allochemical components with respect to cement conditioned the spatial distribution of the microfractures.