Abstract: There are abundant shale oil resources in the seventh member of Yanchang Formation (Chang 7 member) in Ordos Basin. The largescale interlayered type shale oil reserves have been discovered in the first-second sub-member of Chang 7 member (Chang 7_1-2 sub-member), marking a major breakthrough in the exploration and development of continental shale oil. However, there is a low level of systematic study and evaluation of new type shale oil in the third sub-member of Chang 7 member (Chang 7₃ sub-member). By using SEM, 2D NMR, full field fluorescent thin section, and infrared spectroscopy analysis, as well as identification and evaluation techniques such as geophysical exploration and logging, geological understanding and oil enrichment mechanisms are summarized. The analysis shows that: (1) The laminated shale is composed of felsic-rich lamina, organic-rich lamina, tuffaceous-rich lamina, and clay-rich lamina. The pore type is dominated by intergranular pores, dissolution pores, and intercrystal pores, with a porosity of 2%–10% and an oil saturation of 68%–88%. (2) The mud laminar type shale is composed of clayey felsic siltstone, clayey felsic mudstone, and felsic clayey shale. The pore type mainly includes dissolution pores, intercrystal pores, and bedding fractures, with a porosity of 2%–6% and an oil saturation of 65%–75%. (3) The crude oil generated by organicrich shale in Chang 7₃ sub-member was retained and accumulated, and also accumulated in felsic-rich siltstone after micro migration, showing hydrocarbon retention–micro migration and enrichment pattern. The predicted favorable zone of laminated type shale oil in Chang 7₃ submember is 5000 km², and that of mud laminar type shale oil is 1600 km², with predicted reserves of up to one hundred million tons, showing huge exploration potential.

Key words: Ordos Basin, Chang 7₃ sub-member, micro migration and accumulation, laminated type shale oil, mud laminar type shale oil