Quantitative characterization of pore development and its application in shale oil reservoirs of the Qingshankou formation, Songliao basin

The pronounced multi-scale heterogeneity and complex wettability heterogeneity of shale oil reservoirs are key factors governing the distribution and flow behavior of fluids within the pore network. This study focuses on the Qingshankou Formation, Member 1 of the Songliao Basin. Utilizing multifractal theory, it systematically reveals the structural characteristic differences of pores across various scales and with differing wettability, defining geological controlling factors and their significance. Nanoscale fractures are relatively well-developed in both high-organic laminated mixed shale (HCS) and high-organic laminated felsic shale (HQS), with the latter exhibiting superior fracture connectivity and relatively larger average pore diameters for each pore type. Multifractal characteristic parameters indicate that HQS possesses the optimal pore connectivity, while HCS exhibits the poorest connectivity. The content of macropores and felsic minerals jointly controls the pore connectivity characteristics. HQS demonstrates relatively strong oleophilicity, with its oil-wet pores displaying a simple structure and strong connectivity. In contrast, HCS and medium-organic laminated mixed shale (MCS) exhibit relatively strong hydrophilicity, where oil-wet pores feature a complex structure and poor connectivity. High-organic massive felsic mudstone (HQM) and high-organic massive mixed mudstone (HCM) display mixed wettability characteristics. Integrating pore connectivity, wettability, and laminae development characteristics, this study proposes a quality grading method for shale oil reservoirs and provides exploitation recommendations: Type I reservoirs (HQS/MQS (medium-organic laminated felsic shale)) offer superior geological conditions and optimal fracability; Type II reservoirs (HCS/MCS) exhibit the highest geological sweet spot potential but demonstrate poorer fracability; Type III reservoirs (HQM/HCM) lies between the two reservoir types mentioned above. The research findings provide crucial guidance for enhancing the geological understanding of shale oil reservoirs and accelerating their efficient exploration and development.