π-π Stacking in Kerogen and Its Mechanical Impact

Kerogen is a key source of hydrocarbon production through hydraulic fracturing. However, the direct correlation between the molecular structure and mechanical properties remains unclear. Here, we employ four-dimensional scanning transmission electron microscopy (4D-STEM) to reveal heterogeneities defined by the orientation of π-π stacking domains and amorphous regions in kerogen. We observed that the morphologies of π-π stacking domains vary with kerogen maturity, ranging from small, randomly oriented grains to larger, continuous structures. Furthermore, we conduct in situ 4D-STEM tensile testing to visualize the strain distribution across these structural heterogeneities and elucidate the governing deformation mechanisms of kerogen. Our results demonstrate different mechanical responses within kerogen, suggesting that π-π stacking domains contribute to brittleness, while amorphous regions promote ductility. We believe this innovative approach to assessing the correlation between local structural order and the mechanical properties of kerogen could lead to improved geological models for optimizing the hydraulic fracturing efficiency.