Abstract
The second member of the Funing Formation in the Qintong Depression of the Subei Basin is an important potential target for lacustrine shale oil exploration in eastern China; however, systematic understanding of its lithofacies types, reservoir characteristics, and sweet spot distribution remains limited, thereby constraining accurate resource evaluation and exploration deployment. In this study, the second member of the Paleogene Funing Formation was investigated using an integrated approach that combines petrology, geochemistry, mineralogy, physical property analysis, and brittleness index evaluation, leading to the establishment of a ternary lithofacies classification system based on “organic matter abundance–structural characteristics–lithology.” On this basis, the shale reservoir features and sweet spot distribution were systematically characterized. The results show that the shales of this interval are generally characterized by low organic matter abundance, moderate to low thermal maturity, relatively balanced mineral composition, and complex pore structure, which can be further divided into six typical lithofacies. Among them, the medium-organic layered dolomitic shale exhibits superior reservoir quality and fracturability, and is thus identified as the most favorable lithofacies. These findings not only provide scientific support for the selection of favorable areas and efficient exploration and development of shale oil in the Qintong Depression, but also offer a reference framework and methodology for shale oil resource evaluation and sweet spot prediction in similar lacustrine basins.
