Influence of Fractures and Pores on the Mobility of lacustrine shale oil: A Case Study of the Chang 7₃ Black Shale in the Ordos Basin, China

Shale oil mobility critically determines reservoir producibility and is primarily controlled by the fracture and pore systems of shale. However, its behavior in pure shale-type systems remains insufficiently understood. This study investigated the effects of pores and fractures on shale oil mobility based on eight core samples, with and without natural fractures, from the Chang 7₃ sub-member of the Ordos Basin. Geochemical analyses, pore and fracture structure characterization, and T₁–T₂ nuclear magnetic resonance were employed. Results show that fractures significantly enhance shale oil mobility: fractured samples exhibit a movable oil ratio of 55–67%, approximately 3.6 times higher than that of unfractured samples (11–25%). Increased macropore volume, porosity, and permeability markedly promote mobility, whereas higher mesopore specific surface area and macropore fractal dimension suppress it. The positive contribution of macropore volume outweighs the inhibitory effect of fractal complexity, underscoring macropores as key contributors to oil flow. These findings provide critical insights into shale oil mobility in the Chang 7₃ sub-member and establish a scientific basis for identifying sweet spots and optimizing development strategies in pure shale-type reservoirs.