川东红星地区二叠系吴家坪组页岩储层纵向非均质性特征及其发育主控因素

Vertical heterogeneity characteristics and main controlling factors of the Permian Wujiaping Formation shale reservoir in Hongxing area,eastern Sichuan

四川盆地东部红星地区二叠系吴家坪组二段发育一套富硅富碳页岩储层,勘探证实为一套优质含气页岩储层。该套页岩原生品质(有机碳含量、岩矿、沉积构造)纵向具备较强的非均质性,直接影响了页岩储层的含气性和可改造性。在建立页岩等时地层对比格架的基础上,系统阐述了该套页岩储层在岩矿组成、沉积构造、有机质丰度及有机质类型等方面的纵向非均质性。同时从沉积作用、海洋古生产力和氧化还原环境等方面探讨了非均质性的主控因素,明确了其纵向非均质性主要受控于古气候、火山活动及海平面升降等因素,古气候与海平面升降共同控制了陆源碎屑矿物的供给量,火山活动控制了表层海水的古生产力,从而控制了有机质和自生硅质的含量,陆地火山活动和海底火山活动导致页岩储层中发育凝灰岩薄夹层和硅质条带等特殊的岩性夹层,影响了页岩储层自身的可改造性。

A set of silicon-rich and carbon-rich shale reservoirs are developed in the second member of Permian Wujiaping Formation(Wu2 Member)in the Hongxing area of eastern Sichuan Basin,which have been proved to be a set of high-quality gas-bearing shale reservoir based on exploration activities.The set of shale primary quality(organic carbon content,lithology and mineralogy,sedimentary structure)has strong heterogeneity characteristics in vertical direction,directly affecting the gas-bearing property and removability of shale reservoir.Based on the establishment of shale isochronous stratigraphic correlation framework,this study systematically investigates the vertical heterogeneity characteristics of the shale reservoir in rock and mineral composition,sedimentary structure,organic matter abundance and organic matter types.The main controlling factors of heterogeneity are discussed from the aspects of sedimentation,marine paleo-productivity and redox environment.The vertical heterogeneity is mainly controlled by factors such as paleoclimate,volcanic activity and sea level rise and fall.The ancient climate and sea level fluctuations jointly control the supply of terrigenous detrital minerals,volcanic activity controls the paleo-productivity of surface seawater,thereby controlling the content of organic matter and authigenic silica,the continental volcanic activity and submarine volcano activity led to the development of tuff thin interbeds and siliceous strips and other special lithologic interbeds in shale reservoirs,which affected the modifiability of shale reservoirs themselves.