Zhengjian Xu, Xiaodong Hu, Shu Jiang, Xiaogang Li, E Li, Wenchao Zhang, Weisong Wang, Nini Zhang, Yingying Chen, X. Li
High-quality source rocks exert primary control on hydrocarbon accumulations in continental lacustrine basins, particularly for tight sandstone oil reservoirs. The identity of the principal source rocks for the Chang 7 tight oil in the Yanchang Formation, Ordos Basin, and their control mechanisms on accumulation and enrichment remain uncertain. This study integrates gas chromatography-mass spectrometry (GC-MS) analysis of mudstones, oil shales and crude oils with hydrocarbon generation–expulsion simulations, abnormal pressure calculations and fluid-inclusion trapping pressure reconstructions to establish oil–source correlations, characterize primary source rocks and define controlling accumulation mechanisms. Results demonstrate that: (1) the Chang 7 tight oil was sourced predominantly from Chang 7 oil shales in a ‘lower generation–upper reservoir’ configuration; (2) these oil shales are laterally extensive with a substantial thickness (>15 m), high organic matter abundance (average total organic carbon 11.36 wt%), excellent kerogen quality (types I and II 1 ) and moderate thermal maturity (average vitrinite reflectance 0.85%); (3) the cumulative hydrocarbon generation intensity averages 159.46 × 10 4 t km −2 , providing abundant material for tight oil accumulations; (4) source–reservoir pressure differentials (SRPDs) averaging 15.58 MPa have provided the necessary driving force for efficient oil charging into tight reservoirs; and (5) a high-quality oil shale distribution directly governs the tight oil distribution, with transitional zones between hydrocarbon generation centres and high-pressure domains representing optimal enrichment fairways. These findings clarify the fundamental role of lacustrine oil shales in tight oil systems and provide practical guidance for exploration in analogous continental basins.