鄂尔多斯盆地东部下二叠统山西组山2段成岩相划分及展布

Division and distribution of diagenetic facies of the Member 2 of Lower Permian Shanxi Formation in eastern Ordos Basin

鄂尔多斯盆地东部下二叠统山西组山2段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多种成岩作用。在成岩作用研究的基础上,通过大量的岩心观察和薄片鉴定,结合阴极发光、探针分析等方法,将研究区划分出7种单因素成岩相,即:强压实、压溶—石英次生加大、蚀变高岭石、沉淀高岭石、杂基充填、碳酸盐胶结交代、不稳定组分溶蚀成岩相,在此基础上对其进行平面叠加,确定了利于储集层发育的优势成岩相。其中压溶—石英次生加大与杂基、假杂基溶蚀作用的综合作用(叠加和改造)决定了山西组山2段有利的成岩相带,在陕141井区、榆37井区、子洲—清涧地区山西组山2段形成了天然气优质储集层。

The Member 2 of the Lower Permian Shanxi Formation in the eastern Ordos Basin is dominated by quartz sandstones, lithic quartz sandstones and lithic sandstones. The diagenesis includes burial compaction, pressolution, silical cementation, carbonate cementation and replacement, kaolinite cementation, matrix alternation and dissolution. Through the core observations and thin section analyses, combining with cathodoluminescence and scanning electron microprobe studies, seven types of single factor diagenetic facies are identified in the Member 2 of Shanxi Formation in eastern Ordos Basin. They are severe compaction facies, pressolution-quartz overgrowth facies, the kaolinite dissoluted alternation facies, the precipitating kaolinite facies, matrix filling facies, carbonate cementation and replacement facies and dissolution facies. Furthermore the planar superimposition was made and the favorable diagenetic facies for reservoir development was determined. The combination of pressolution-quartz secondary overgrowth and pseudomatrix dissolution determined the favorable diagenetic facies belt of the Shanxi Formation. High-quality reservoirs in the Member 2 of the Shanxi Formation are distributed in Shaan 141 well area, Yu 37 well area, and Zizhou-Qingjian area.