Rock-physics-guided evaluation of source-reservoir coupling in lacustrine self-sourced shales: A case study of Shahejie Formation in Dongpu sag

Despite its significant progress, current geological evaluation of source-reservoir coupling in lacustrine shales predominantly focuses on macroscopic description and qualitative analysis. The lack of a quantitative parameter system that can directly support sweet spotting restricts the practical application of the evaluation results in effectively guiding exploration and development. Targeting the Shahejie Formation in the Dongpu sag, this study identifies a typical self-sourced pattern for shale oil and gas based on a comprehensive core analysis of the source and reservoir characteristics. Building on this, porosity and total organic carbon (TOC) content are integrated and defined as the source-reservoir coupling coefficient (SRCC), which is adopted as a key parameter for geological sweet-spot evaluation. To achieve quantitative SRCC evaluation, an exponential model is established, using rock physics experimental data, to predict SRCC from vertical P-wave velocity. An analysis of the cumulative frequency distribution of SRCC leads to the establishment of thresholds at 2.1 and 0.7 to delineate three classes (Class I, II, and III) of source-reservoir configurations. Single-well evaluation suggests that Classes I and II are dominant in Zone 3 of the upper Sha4 Member. Class-I intervals, comprising two predominant lithofacies of laminated argillaceous mixed shales and laminated calcareous mixed shales, exhibit both high hydrocarbon generation potential and promising reservoir properties. These findings provide a foundation for optimizing sweet-spot prediction and designing horizontal well target windows in the Qianliyuan sub-sag.