Current status, advances, and prospects of CNPC’s exploration of onshore moderately to highly mature shale oil reservoirs

China National Petroleum Corporation(CNPC)boasts abundant continental shale oil resources in areas covered by its mineral rights. The national hydrocarbon resource evaluation of the 13th Five-Year Plan reveals that CNPC’s geological resources of onshore moderately to highly mature shale oil(hereinafter referred to as shale oil)are estimated at 201×10⁸ tonnes, accounting for 71 % of the national total. Shale oil production has increased significantly in key plays such as the 7^th member of the Yanchang Formation in the Ordos Basin, the Qingshankou Formation in the Songliao Basin, and the Lucaogou Formation in the Junggar Basin, rising from 2.5×10⁴ tonnes in 2010 to 391.6 ×10⁴ tonnes in 2023, suggesting enormous potential for shale oil exploration. The study results reveal that CNPC’s commercial exploration of continental shale oil is facing challenges in both geological understanding and techniques due to the highly heterogeneous geological characteristics and significantly different factors determining the enrichment and high productivity across various types of continental shale oil reservoirs. Notably, despite large-scale exploration in the 1^st and 2^nd submembers of the 7^th member of the Yanchang Formation in the Ordos Basin, intercalated shale oilreservoirs exhibit greatly varying drilling ratio for targets under exploration, limited research on fine-grained sedimentary sequences of deep lacustrine facies, and the low accuracy of techniques for characterizing the spatial distribution of targets. Shale oil reservoirs of the mixed type exhibit great vertical thicknesses, frequent lithological variations, and multiple suites of sweet spots. Despite breakthroughs in the Qaidam and Bohai Bay basins, the exploration of these reservoirs is constrained by greatly different vertical shale oil production in geological sweet spots, ambiguous major factors contributing to high shale oil production, and imperfect techniques and methods for evaluating and selecting dominant targets. For the exploration of shale oil reservoirs of the pure shale type, breakthroughs have been achieved in the Gulong shale oil reservoirs of the Qingshankou Formation in the Songliao Basin. Nevertheless, due to greatly different hydrocarbon generation and expulsion characteristics and significantly varying in-situ hydrocarbon retention across various types of shales in continental lacustrine basins, it remains necessary to further investigate the geo-engineering integrated techniques and methods for target evaluation. Overall, CNPC’s exploration and exploitation of shale oil reservoirs are still rapidly advancing. In the future, it is necessary to intensify research on the genetic mechanisms of various sand bodies in deep parts of fresh lacustrine basins to achieve the commercial exploration of intercalated shale oil reservoirs such as thinly laminated turbidite sand bodies. For shale oil reservoirs of the mixed type, there is a need to enhance the evaluation of source rock-reservoir assemblages of these reservoirs enriched in carbonate in saline lacustrine basins. This will enable the preferential selection of primary targets for efficient exploration. Furthermore, differential evaluations of hydrocarbon generation and expulsion should be underlined for high-quality source rocks in both fresh and saline lacustrine basins to identify the optimal targets. The purpose is to achieve geo-engineering integrated, fine-scale exploration of shale oil reservoirs across various types of lacustrine basins.