准噶尔盆地乌夏地区二叠系沉积特征及有利储集层

Sedimentary Features and Favorable Reservoirs of Permian in Wu-Xia Area of Junggar Basin

准噶尔盆地乌夏地区二叠纪处于前陆盆地的早、中期,受断层活动、火山作用和物源等不同因素影响,早二叠世发育了一套由火山岩向火山碎屑岩、正常碎屑岩过渡的岩性组合,火山作用总体向上逐渐减弱。中、晚二叠世前陆盆地逐渐向坳陷盆地过渡,其中风城组沉积期为二叠纪最大湖侵期,沉积中心向南迁移;夏子街组沉积期和下乌尔禾组沉积期广泛发育扇三角洲-湖泊相沉积组合,自下而上为基准面上升-下降-上升的旋回。岩性和构造控制了火山岩储集层的发育,沉积相则控制了碎屑岩储集层的发育。水下分流主河道砂体的粒内溶孔、构造活动带火山碎屑岩的裂缝、深层火山岩中的气孔是最为有利的储集空间。

The Permian of Wuerhe-Xiazijie （Wu-Xia） area in Junggar basin was in the early-middle period of foreland hasin. Being affected by different factors, such as fault movement, volcanic action and sedimentary source, in the Early Permian, there developed volcanic rock, pyroclastic rock and normal clastic rock. The volcanic action was weakened gradually upward. In the Middle-Late Permian, the foreland basin changed to down-warped basin gradually. And its Fengcheng depositional stage there was a big lake transgression and the depocenter migrated to the south. In Xiazijie depositional stage and Lower Wuerhe depositional stage, there widely developed fan delta and lacustrine facies assemblage with a basal level cycle of ascending- descending- ascending from bottom to top. The development of volcanic reservoirs are controlled by lithology and structure, while that of clastic reservoirs by sedimentary facies. In general, the most favorable reservoir space types include the intragranular dissolved pore in the sands of underwater distributary channel of fan delta front, the fissures of pyroclastic rock in mobile belt and the vesicular pore of volcanic rock in deep zone.