A Compositional and Genetic Framework for Shale Lithofacies Classification and Reservoir Quality Prediction: Insights From the Wufeng‐Longmaxi Formation, South Sichuan

ABSTRACT Although shales are of fundamental importance in geological research and energy exploration, no consensus has been reached on a unified classification and nomenclature that adequately reflect their multiscale heterogeneity and genetic origins. To address this gap, we propose a novel framework grounded in mineralogical and genetic perspectives, aiming to advance shale characterisation and standardisation, and to improve the evaluation of shale reservoir quality. Within this framework, quartz—the dominant component of organic‐rich shales—is subdivided into intrabasinal authigenic particles and extrabasinal detritus, with their relative contributions quantified. Excess silica, representing authigenic quartz including microcrystalline and biogenic forms, is employed as a key parameter for classification. When excess silica exceeds 50% of total quartz, shales are defined as siliceous shales , whereas those with excess silica below 50% but total siliceous minerals (quartz and feldspar) exceeding 50% are classified as silty shales . Shales with mixed compositions are categorised separately. Our results reveal that siliceous shales exhibit the greatest development potential, followed by silty shales with high total organic carbon and finally mixed shales. This scheme not only discriminates shales with different sedimentary backgrounds, total organic carbon levels, and quartz sources, but also provides a genetically informed and practical tool for predicting shale reservoir quality. By integrating mineralogical composition and genetic origins, the proposed framework offers a systematic alternative to existing classification approaches.