The potential evaluation of shale oil in the seventh member of Dameigou Formation(J₂d⁷)on the northern margin of Qaidam Basin: A case study of Dameigou area

This study used 40 shale samples from the seventh member of Dameigou Formation in 4 drilling wells and the Jurassic standard profile in the Dameigou area to illustrate the organic geochemical characteristics, the petrographic and mineralogical features, and the reservoir properties. According to the results obtained, the average content of total organic carbon is 5.22%; the kerogen is of I-II type, dominated by sapropel; the average value of organic maturity is 0.52%, belonging mainly to immaturity to low maturity; the reservoir space has various types, and micro-fractures are developed in favor of the adsorption and storage of the shale oil, and the content of brittle minerals in the mineral composition is more than 40% in favor of the production fracturing in the future. In addition, the fracture surface and the bedding planes with fluorescent provide the direct evidence for the presence of shale oil. A comprehensive analysis shows that the seventh member of the Dameigou Formation in Dameigou area with the geological conditions of the shale oil formation is the most favorable section for the development of Middle Jurassic shale oil. Moreover, the single layer of the shale in this member has larger thickness and the lateral distribution of this member is stable in the plane within the northern margin of Qaidam Basin. Combined with the existing results, it is tentatively held that the favorable areas for the shale oil development are Lenghu area, Saishiteng depression, Yuka depression and Dachaidan-Dameigou area.