Multiscale Mechanical Characterization of Krol Shale Using Brazilian Tensile Strength and Nanoindentation Tests: Implications in Hydrocarbon Recovery and CO ₂ Sequestration

Multiscale mechanical characterization of organic-rich shale is crucial for designing effective and safe rock-engineering practices during hydrocarbon exploration and for long-term CO 2 sequestration. This study employed a conventional macroscopic Brazilian Tensile Strength (BTS) test and a nonconventional microscopic nanoindentation test to understand the multiscale mechanical behavior of untapped Krol shale from the Lesser Himalaya. The studied shale with gas potential exhibits significant mechanical heterogeneity influenced by its prolonged tectonic history, including multiple thrusting events and intense fracturing. Results indicate consistently low elastic ( E ) modulus values across scales, suggesting low-to-moderate stiffness and a semiductile nature. Despite the presence of brittle mineral phases such as quartz and feldspar, nanoindentation results predominantly reflect lower modulus values associated with clay minerals and organic matter, indicating substantial microstructural alteration due to prolonged tectonic history. Brittleness index (BI) values derived from both BTS and nanoindentation load–displacement curves consistently indicate semiductile behavior. Additionally, Atomic Force Microscopy (AFM) analysis reveals pronounced surface heterogeneity, characterized by high roughness and dense asperity distributions, which may act as localized stress concentrators and facilitate microcrack initiation. To bridge the gap between scales, multiscale integration was carried out using a probabilistic distributional approach, in which microscopic BI and E data were modeled with a Gumbel extreme-value distribution and upscaled to the macroscopic level using a scaling factor. The predicted macroscopic BI and E show strong agreement with experimental results, confirming the robustness of the integration approach. This multiscale mechanical characterization and integration approach offers important implications for the safe and effective hydrocarbon recovery, as well as for ensuring the long-term reliability of CO 2 storage in shale formation.