Lacustrine shale oil enrichment in China: mechanisms, key assessment proxies, and a novel framework for rapid evaluation

Lacustrine shale oil has become an increasingly important contributor to oil supply in China, yet its enrichment mechanisms remain more difficult to generalize than those of marine shale systems because of stronger heterogeneity, more variable organic matter inputs, and wider maturity ranges. Although numerous case studies have investigated the factors controlling shale oil enrichment, existing strategies for evaluating potential targets still rely heavily on empirically selected parameters (such as TOC content, S 1 value, and OSI ratio) and basin-specific experience. As a result, a conceptual screening framework for evaluating potential targets in lacustrine shale oil systems remains insufficiently developed. This study synthesizes current knowledge of lacustrine shale oil systems in China and establishes an integrated framework for understanding their enrichment mechanisms. Four controlling factors are identified: hydrocarbon generation, storage capacity, preservation conditions, and fracability coupled with dynamic enrichment (fluid properties and oil mobility). Correspondingly, the key geological and geochemical proxies used in potential target evaluation are systematically summarized, and their geological significance, applicability, and limitations are clarified. On this basis, Rock-Eval pyrolysis is further positioned as a practical and cost-effective screening tool, from which an operational workflow is developed to support the rapid identification of potential intervals. Another central contribution of this study is the reinterpretation of T max value suppression in shale oil systems, a phenomenon that has traditionally been regarded in conventional petroleum systems as an anomaly that hinders the objective assessment of thermal maturity. Here, we show that, under geological conditions favorable for lacustrine shale oil enrichment, T max value suppression may instead serve as a potential screening indicator of oil enrichment and help identify intervals warranting further evaluation. Building on this insight, a four step T max value suppression-based workflow for shale oil exploration potential evaluation is proposed: recognition of anomalous T max values, data-quality screening, exclusion of kerogen and mineral-related effects using multiple constraints, and cross-checking with complementary parameters. A detailed examination of the Paleogene Shahejie Formation in the Bohai Bay Basin illustrates the potential applicability of this approach, while evidence from three additional lacustrine shale systems in China further supports its potential applicability across different lacustrine settings. This study links enrichment mechanisms, assessment proxies, and operational decision-making within a unified framework for lacustrine shale oil enrichment. The proposed workflow not only refines the geological interpretation of Rock-Eval parameters, but also provides a rapid and practical screening approach that helps identify intervals requiring further geological, geochemical, and engineering evaluation.