关键词: 碱湖, 页岩油, 甜点, 混积岩, 玛湖凹陷, 风城组, 准噶尔盆地

Abstract: Although alkaline lake type shale oil has a broad resource prospect, its reservoirs are different from the classic shale oil reservoir due to multisource mixed sedimentation, and the genesis of "sweet spot" reservoirs is extremely complex. It is urgently needed to perform a study on the sweet spots of alkaline lake type shale oil, as a supplement for the research of continental shale oil. Based on core observation, thin section identification of rock, whole-rock X-ray diffraction and Formation Micro Imager (FMI) logging, the paper investigates the classification and main controlling factors of sweet spots of alkaline lake type shale oil in Fengcheng Formation of Mahu sag in Junggar Basin. The results show as below. According to the composition and content of the main minerals, the alkaline lake deposits of Fengcheng Formation can be divided into 7 types of fine-grained sedimentary rocks. Aaccording to the rock type of shale oil occurrence, the sweet spots can be divided into three types, i.e., mixed type, endogenous control type and terrigenous supply type. The mixed type is mainly and comprehensively controlled by rock structure, organic matter abundance, fracture, and dissolution. The endogenous control type is mainly controlled by rock composition, fracture, and dissolution. The terrigenous supply type is comprehensively controlled by rock structure, mineral composition, and dissolution. The three types of sweet spots are regularly distributed in Mahu sag of Junggar Basin. They are distributed in the shallow lake area of foreland slope, the deep lake area of foreland depression, and the transition area between the steep slope and the deep lake area, respectively. The mixed type is the primary target for exploration and development of the alkaline lake type shale oil in Fengcheng Formation of Mahu sag.

Key words: alkaline lake, shale oil, sweet spot, mixed sedimentary rock, Mahu sag, Fengcheng Formation, Junggar Basin