准噶尔盆地玛北地区夏203井风城组混积页岩储层特征及主控因素OA

The Fengcheng Formation in the Mahu Sag of the Junggar Basin is a set of mixed sedimentary strata formed in an alkaline saline lake.Among them,the Mabei area is currently the main target for shale oil exploration in the Fengcheng Formation.The continuous breakthroughs in shale oil exploration in the Mabei area demonstrate the broad exploration prospects of shale oil in this region.However,the special sedimentary and diagenetic backgrounds of the alkaline lake have led to the strong heterogeneity of the Fengcheng Formation,which restricts the exploration and development of shale oil.To clarify the development characteristics of the Mabei shale oil reservoir,this study selected a 237.25 m core from well Xia-203 for full-diameter core dual-energy CT scanning,automatic mineral analysis(MaipScan),two-dimensional large-area scanning imaging(Atlas)and other test analyses.The following conclusions were drawn:1)laminar fractures are the main macroscopic reservoir spaces.Oblique fractures can connect laminar fractures,resulting in vertical communication between laminations.Laminations mainly developed during the stage of frequent climate fluctuations in the second member of the Fengcheng Formation.The main types of laminations include siliceous-rich laminations,carbonate-rich laminations,and felsic laminations.2)The mineral composition is characterized by low clay minerals and rich brittle minerals,which lays the foundation for the fracturability of the Fengcheng Formation.The fine-grained rocks in well Xia-203 are mainly siliceous shale,carbonate-rich siliceous shale,and silica-rich carbonate shale.3)Intergranular pores,intergranular dissolved pores and organic matter pores are the main microscopic reservoir spaces.The contents of intergranular pores and intergranular dissolved pores depend on the content of felsic minerals;the content of organic matter pores depends on the content of organic matter and the occurrence mode of organic matter.The overall porosity and the proportion of organic matter in layers 8～12 are higher than those in other layers,making them the development intervals of high-quality shale reservoirs.4)The vertical distribution of favorable shale reservoirs is jointly controlled by the input of terrigenous clastic materials,volcanic activities and climate fluctuations.During the stage when the Middle Fengcheng Formation was deposited,the small input of terrigenous clastic materials promoted the formation of shale reservoirs.The devitrification of volcanic materials and the released silica provided abundant siliceous sediments.Frequent climate fluctuations and the oscillatory nature of the lacustrine basin promoted the development of laminations.Microscopic pores and macroscopic lamination fractures together form a pore-fracture reservoir space system.The research results provide theoretical guidance for the further exploration and design of development plans for alkaline lake shale oil in the Mabei area.