关键词: 准噶尔盆地, 三工河组, 储层, 成岩作用, 成岩控制因素

Abstract: In Junggar Basin, the present geothermal gradient is low (ca. 2.3℃/hm), and the braided river delta sandbody of Jurassic Sangonghe Formation on the west side of its hinterland has a great difference in burial depth (ca. 2 100 m); the complicated diagenesis has influences on hydrocarbon exploration and development deployment. Using rock thin sections, cathode luminescence, scanning electron microscopy and fluorescent microscopic identification of fluid inclusions, in combination with the evolution characteristics of clay minerals, the paper analyzes the differential diageneses, diagenetic stages and the controlling factors of the Sangonghe Formation reservoirs in Shawodi, Moxizhuang, and Zhengshacun areas on the west side of the hinterland of Junggar Basin. The diagenesis of the Sangonghe Formation reservoirs on the west side of the hinterland of Junggar Basin is mainly controlled by multiple factors such as burial depth, detrital component of sandstone, geothermal gradient, and hydrocarbon charging. The tectonic movement during Himalayan epoch caused great differences in burial depth between various small blocks, which is the main factor restricting their differential diagenesis. In Sangonghe Formation of Shawodi and Moxizhuang areas, the weak compaction of sandstones is caused by shallow burial depth, and calcite cementation and kaolinite cementation are the dominant diagenesis types, which is in the periond between the Stage B of early diagenesis and Stage A of middle diagenesis. The reservoir space is dominated by primary pores. Sangonghe Formation in Zhengshacun area has a larger burial depth, showing the significant compaction of sandstones; dolomite and ferrodolomite are the main cements, and the content of illite is high. It can be observed that plenty of secondary pores are formed by the dissolution of feldspar; when reaching the Stage B of middle diagenesis, primary pores are extremely undeveloped, and the reservoir space is dominated by secondary dissolved pores. The composition of sandstone debris is the material basis of diagenesis. The higher the content of plastic debris, the weaker the ability of sandstone to resist compaction is. The low geothermal gradient in Junggar Basin delays the compaction and maturation of organic matter in Sangonghe Formation, which is an important reason for the middle diagenetic stage of the Sangonghe Formation reservoirs in the hinterland of Junggar Basin under deep buried conditions. Analysis of burial history shows that overpressure effectively delays the compaction intensity of the Sangonghe Formation reservoirs in the hinterland of Junggar Basin. Three stages of oil and gas charging since Late Cretaceous have inhibited the occurrence of cementation to varying degrees, and promoted the dissolution of calcareous cements, potassium feldspar and rock debris in the Sangonghe Formation reservoirs.

Key words: Junggar Basin, Sangonghe Formation, reservoir, diagenesis, controlling factors of diagenesis