鄂尔多斯盆地安塞—神木地区山西组成岩与沉积相耦合关系

通过岩心描述、薄片观察、阴极发光、探针分析等多种方法,研究了鄂尔多斯盆地安塞-榆林-神木地区二叠系山西组山2段储集层岩石类型、成岩作用类型及其分布.研究区岩石类型主要为石英砂岩、岩屑质石英砂岩和岩屑砂岩,储集层经历了压实、压溶、硅质胶结、碳酸盐胶结交代、高岭石胶结、杂基蚀变以及溶蚀等各种成岩作用,其中溶蚀作用是控制有效储集层形成的主要成岩作用.同时对成岩作用的平面分布特征进行了详细分析,认为成岩作用在区域内的分布主要受沉积相带的控制,顺沉积体系方向,成岩作用表现为压溶-硅质胶结、溶蚀作用增强,压实、碳酸盐胶结交代作用减弱,由河道中心向侧翼方向,压实、碳酸盐胶结、杂基蚀变作用增强,硅质胶结、溶蚀作用减弱.孔隙主要发育于顺沉积体系方向的三角洲平原分流河道、前缘水下分流河道、河口坝砂体中.图5表1参40

Coupling of diagenesis and sedimentary facies of Shanxi Formation in An' sai-Shenmu, Ordos Basin

The type of rocks, diagenesis, distribution of Permian Shan 2 Member in the central-eastern Ordos Basin were studied based on core observation, thin section analysis, cathodoluminescence and scanning electron microprobe. The reservoir mainly consists of quartz and feldspathic quartz sandstones with subordinate lithic sandstones. The sandstones experienced all kinds of diagenetic processes, such as mechanical compaction, pressure solution, quartz overgrowth, carbonate cementation and replacement, kaolinite filling, dissolution. The dissolution turns out to be the essential control for the formation of effective reservoirs. Laterally, diagenetic features were analyzed in detail, with a conclusion that the regional variations of diagenesis are mostly controlled by facies in the given area. Along the dispersal system of sediments, pressure solution-siliceous cementation and dissolution become prominent whereas compaction, carbonate cementation and replacement decrease in intensity. From the center of the distributary channels to both flanks, compaction, carbonate cementation, and matrix dissolution increase in intensity and siliceous cementation and dissolution wane accordingly. Pores are well developed in the sandstones in the distributary channel of deltaic plain, the subaqueous distributary channel and mouth bar of deltaic front.