Fractal characteristics and controlling factors of coal bearing shale pores in the continental fault depression basin

ABSTRACT This study investigates coal-bearing shale from the Cretaceous Shahai Formation in the Fuxin Basin using TOC analysis, mineral composition testing, and low-temperature N₂ adsorption to explore pore structure, fractal characteristics, and their controlling factors. Results show that TOC varies significantly (average 3.41%) and shale contains abundant clay minerals (average 40.91%). The pores are dominated by ink-bottle-shaped pores with narrow necks and wide bodies, parallel-plate pores, and clay-related slit pores. The shale exhibits dual fractal behavior, with average D1 ≈ 2.5 and D2 ≈ 2.7, indicating that internal pores are more complex than surface structures. Micropores contribute the most to fractal dimension, with correlations of 0.6384 and 0.8359 with fractal dimensions D1 and D2, respectively. They are the main source of pore heterogeneity and complexity. Thermal evolution of organic matter promotes micropore development and increases internal structural complexity. Carbonate cement enhances micropore growth and overall complexity, whereas weak anti-compaction capacity of clay leads to particle alignment during diagenesis, reducing pore volume and simplifying morphology, thus decreasing pore complexity.