Multi-scale control of initial porosity distribution on deformation processes in a heterogeneous porous carbonate rock

Understanding the mechanical behavior of porous carbonate rocks is critical for improving reservoir management and developing sustainable energy solutions. Carbonate rocks are formed through complex sedimentary processes and diagenesis, leading to significant microstructural variability at multiple scales, which influences their mechanical properties. This complexity necessitates advanced experimental tools to accurately describe their behavior under various stress conditions. 

Recent studies have demonstrated that strain is accommodated heterogeneously in porous sedimentary rocks, such as sandstones and limestones. Precisely, formation of deformation bands has been observed under various loading conditions in porous limestones which can significantly affect the capacity, i.e., porosity, and thus permeability, of carbonate reservoirs. The inherent multi-scale nature of carbonate microstructure and deformation bands – from the grain to the reservoir scale – leads to a lack of comprehensive and high-quality data on the relationship between deformation modes and microstructure, despite significant advancements in the field. We propose to carry out extensive experimental investigations on a material at multiple scales and various loading conditions. 

This work explores empirically the relationship between the initial porosity distribution of the heterogeneous Saint-Maximin limestone and the deformation modes observed from the micrometer to the centimeter scale. At the standard laboratory centimeter scale, it was shown that the band pattern was controlled by the porosity heterogeneity at the centimeter scale, and initiated preferably in the zones of lower porosity, showing first order control of porosity at this scale. The abundance of SML experimental data and its heterogeneity were key advantages for exploring strain accommodation at lower scales. By conducting a series of in situ tests on smaller, 8 mm in diameter samples, we aimed to elucidate the role of porosity heterogeneity in the onset and propagation of deformation bands, thus enhancing our understanding of the mechanical processes governing carbonate rocks. Ultimately, the results could contribute to improved modeling of multiscale geosystems.