Introducing an Enhanced Cumulative Size Distribution Model to Unearth the Origins of Macropore Heterogeneity of the Chang-7 Shale Oil Reservoirs in the Ordos Basin

Characterizing the fractal nature of shale pores is critical for understanding their heterogeneity, which significantly impacts hydrocarbon mobility. A critical technique in this analysis involves the digital evaluation of scanning electron microscopy (SEM) images. While the cumulative size distribution model is a viable method in SEM fractal analysis, its accurate application necessitates exhaustive microimaging of entire sample cross-sections, rendering it impractical. To address this challenge, we propose an innovative approach that develops a universal equation for this model, along with numerical solving methods. This approach expands the model’s applicability, enabling accurate fractal analysis of entire samples using only randomly selected microscopic fields. It enhances the existing framework for fractal modeling and potentially serves as a valuable tool for studying fractal structures. Using this method, we investigated the fractal characteristics of various macropore types across different lithological units in the Chang-7 shale of the Ordos Basin. Our findings indicate that macropore heterogeneity is influenced by variations in pore type composition, their response under compaction, and organic acid dissolution, all of which are driven by differences in lithology. These findings provide new insights into the mechanisms driving macropore heterogeneity from the perspective of lithological and pore-type variations, potentially yielding valuable implications for the exploration and development of Chang-7 shale oil.