Microscopic Occurrence Characteristics of Oil in Different Shale Lithofacies of the Q ingshankou F ormation, S ongliao B asin: Insights From Laser Scanning Confocal Microscopy Freezing Observation Technology

ABSTRACT The Qingshankou Formation shale in Songliao Basin exhibits strong heterogeneity of mineral compositions and lithofacies, resulting in significant variations in oil mobility across different shale lithofacies and critically impacting the prediction of shale oil sweet spots. In this study, optical observation and laser scanning confocal microscopy (LSCM) freezing observation technology were employed for characterising microscopic occurrence states of oil in different shale lithofacies, thus evaluating shale oil sweet spot intervals. Six lithofacies have been identified, including high‐TOC laminated argillaceous mudstone, high‐TOC laminated siliceous mudstone, moderate‐TOC laminated siliceous mudstone, high‐TOC massive siliceous mudstone, high‐TOC massive dolomitic mudstone and moderate‐TOC massive calcareous mudstone. Shale oil mainly occurred in the form of irregular shapes (such as isolated star points, clusters, and large areas of continuous sheets) in the interparticle pores and intraparticle pores. In different shale lithofacies, the relative abundance and distribution of light oil and heavy oil components show strong heterogeneity. Among them, the high‐TOC laminated siliceous mudstones display relatively high TOC contents, which have great hydrocarbon generation potentials, as well as well‐developed storage networks consisting of bedding‐parallel fractures and micro‐to‐nano‐sized pores, providing excellent storage spaces for shale oil. Moreover, the high‐TOC laminated siliceous mudstones have higher abundances of light oil, making it a favourable lithofacies for shale oil exploration and development in Songliao Basin.