Shale Pore Investigation beyond the Practical Pore Resolution Limits of Scanning Electron Microscopy

Characterizing diverse pore types is essential for optimizing resource exploration in shale formations. Scanning electron microscopy (SEM) is the primary tool for this analysis; however, its practical pore resolution (PPR) limit of 30 nm hinders the quantitative analysis of smaller pores. To address this challenge, we introduced a method for characterizing mesopores below the SEM’s PPR threshold, focusing on the interclay mineral mesopores in Chang-7 shale as a case study. We employed low-pressure nitrogen adsorption and SEM to analyze the overall mesopore structures, confirming their self-similarity and dominance of interclay mineral mesopores. SEM digital analysis was used for the quantitative examination of interclay mesopores exceeding the PPR threshold. Additionally, a fractal model was developed using data from these larger mesopores and their fractal properties to predict the size distribution of super-PPR mesopores (2–30 nm). To validate this approach, we applied a same modeling method to predict the pore size distribution in the 30–60 nm range, and compared these predictions with measured values. With relative root-mean-square error (RRMSE) values ranging from 9.98 to 19.80%, our approach demonstrates high accuracy. This research advances mesopore characterization methods and offers deeper insights into hydrocarbon mobility and pore genesis in shale formations.