Integrative Analysis of Mechanical Heterogeneity in Organic-Rich Shales: Bridging Nano- and Macroscale Properties for an Enhanced Geomechanical Understanding

Understanding the mechanical properties of shale is critical for hydraulic fracturing and rock physics modeling. However, the complex and heterogeneous nature of the shale matrix poses significant challenges for analyzing its behavior across various scales. This study introduces a method for investigating the mechanical heterogeneity of samples from Eagle Ford shales using a combination of nano-indentation and macroscopic mechanical testing. The results reveal a dual-peak distribution in the nanoscale measurements for Young's modulus and hardness properties, indicating a comparable frequency of soft and hard constituents, validated by SEM mapping. Young's modulus and hardness values exhibit significant mechanical heterogeneity at the nanoscale level, varying between 7–85 GPa and 0.3–4.9 GPa, respectively. Meanwhile, macroscale yield displays a normal distribution for Young's modulus values ranging from 25 to 60 GPa, representing the overall behavior of mechanical properties. The properties at different locations within the core plug at the nanoscale were statistically correlated with macroscopic properties. The study revealed that the macroscopic behavior is influenced by both soft and hard components in proportions corresponding to their frequencies. The reported outcomes provide valuable insights for improved modeling and the design of stimulation processes to exploit shale resources further.