Lacustrine fine-grained sediments are developed in Member 3 of Shahejie Formation of Qibei subsag of Qikou sag, with good source rock quality and rich in shale oil resources. However, the corresponding research is still in the early stage. As stimulated by the industrial development of lacustrine shale oil in Member 2 of Kongdian Formation of Cangdong sag, it is inevitable to implement the exploration prospects of fine-grained sediments. In order to explore the geological characteristics and exploration potential of shale oil in Member 3 of Shahejie Formation of Qibei subsag, based on the cores, analytical tests, logging data and logging data of the wells such as F39X1 and QY10-1-1, a comprehensive study is carried out on the geological characteristics, shale oil types and enrichment patterns of the shale strata in Member 3 of Shahejie Formation, and the spatial distribution of sweet spots. There are various mineral compositions and rock types in Member 3 of Shahejie Formation of Qibei subsag, mainly including calcareous-dolomitic shale, felsic shale, hybrid shale, micritic dolomite, sparry bioclastic dolomite, and siltstone. The total organic carbon (TOC) content of source rocks is mainly distributed between 1% and 3%, dominated by type Ⅱ kerogen, and the vitrinite reflectance (Ro) is generally higher than 0.7%. The reservoir spaces mainly include intergranular pores, intercrystalline pores, biological cavity pores, organic pores, bedding fractures, and structural (or microstructural) fractures. The shale oil presents obvious crossover effect (with an average oil saturation index of 116.3 mg/g), as well as good fluorescence effect. This study identifies two types of shale oil, i.e., monolayer type and interbedded type, in Member 3 of Shahejie Formation in Qibei subsag, constructs two enrichment patterns, i.e., high-TOC retention-type and low-TOC migration-type shale oil, and establishes the quantitative evaluation methods and standards of sweet spot based on multiple parameters such as oil saturation index, TOC and brittleness index. For the horizontal well QY10-1-1 deployed in the sweet spot, the initial oil production is calculated to be 103.5 t/d; it is expected to form a new field with the increasing reserves of 100 million tons. It is confirmed by the exploration discovery that the fine-grained rock section of Member 3 of Shahejie Formation in Qikou sag has good exploration potential for shale oil.
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