Correlation Classification and Genetic Mechanism of Shale in Rift‐Lacustrine Basins

ABSTRACT Shale oil reservoirs in rift‐lacustrine basins exhibit significant heterogeneity due to complex sedimentary origins; however, the mechanisms controlling their spatial distribution remain unclear. Taking the Upper Submember of the fourth member to the Lower Submember of the third member of the Shahejie Formation in the Shengtuo Area of the Bohai Bay Basin as the study interval, this study proposes a lithofacies classification framework that integrates structural configuration (interbed distribution patterns, sandy interbeds content) with mudrock quality parameters (TOC and carbonate content). Utilising petrological datasets—core observations, thin‐section petrography, well‐log interpretations and X‐ray diffraction analysis—six lithofacies associations are identified, with spatiotemporal distributions mapped across depositional environments depicted. By analysing its distribution mechanism, a depositional model of shale oil reservoir lithofacies association controlled by terrestrial input was established. Vertically, increasing sediment supply results in a stratigraphic succession progressing from basal endogenic lithofacies associations through mixed‐source lithofacies associations to uppermost terrigenous lithofacies associations. Laterally, the distribution of depositional systems is controlled by terrigenous clastic inputs; therefore, the proximal turbid water zone primarily develops conventional reservoir units and the semi‐turbid zone progressively transitions into lithofacies associations of gravity flow origin and mixed‐source coupled origin. In contrast, the distal clear water zone preserves lithofacies associations of endogenic bio‐chemical origin. In the plane, terrigenous lithofacies associations are predominantly distributed at paleogully termini, while mixed‐source lithofacies associations occupy paleogully flanks. Concurrently, endogenic lithofacies associations characterised by authigenic mineral precipitation are developed within the southern lacustrine. This study offers theoretical foundations for elucidating reservoir heterogeneity formation and predicting shale oil sweet spots in rift‐lacustrine basins.