Differences and genesis of shale oil properties between the upper and lower sections of the Lucaogou Formation in the Jimsar Sag

Abstract

The Lucaogou Formation is a set of saline lake sediments with high abundance of organic matter and good parent material type in the Jimsar Sag, Junggar Basin. It belongs to the best source rock. The Lucaogou Formation sandstone and shale are thinly interbedded, and the upper and lower reservoirs are oil-bearing as a whole, with source-storage integration characteristics. The upper part of the shale oil and the lower part of the shale oil in the Lucaogou Formation are more heavily oily, and the lower part of the oil is heavier. Fine geochemical analysis shows that the crude oil in the upper part of the Lucaogou Formation is formed in a sedimentary environment with certain reduction, while the lower crude oil is formed in a highly reducing and salinized environment; The parent material in the upper and lower shale oil sources in the Lucaogou Formation is mainly algae and lower aquatic organisms, but the lower aquatic organisms in the lower part are obviously dominant, and the upper and lower raw materials are significantly different. The difference of the characteristics of the shale oil in the upper and lower parts of the Lucaogou Formation is closely related to the sedimentary environment of the source rock and the source material. At the same time, the special source of the lower part of the Lucaogou Formation produces hydrocarbons in the early stage of the lower evolution stage, which makes the oil quality of the crude oil become heavier obviously.