准噶尔盆地车排子周缘白垩系底部不整合面的形成及其油气输导作用

Formation of Unconformity Surface at Cretaceous Bottom and Its Significance for Hydrocarbon Migration in Chepaizi and Its Surrounding Areas of Junggar Basin

准噶尔盆地白垩系底部不整合面在车排子周缘大面积分布,是其二叠系和侏罗系的油源进入白垩系和新近系储层的重要通道之一,对其微观结构和几何形态的研究对油气勘探有重要意义。利用岩心、测井、岩屑录井等资料识别出不整合面的三层结构,对不整合面之上的岩石、风化粘土层及不整合面之下的半风化壳进行深入研究,探讨白垩系底部不整合面的形成过程,明确不整合面三层结构的油气输导作用。不整合面的形成可划分为抬升风化期、剥蚀搬运期、下降沉积期和成岩压实期4个阶段。研究表明风化粘土层上下的岩石具有高效的油气输导能力,风化粘土层在断裂不发育区可作为油气局部盖层。油气沿白垩系底部不整合面从东南向西北部的车排子凸起运移。

The unconformity surface at Cretaceous bottom, which widely develops in Chepaizi area of Junggar Basin, is one of the most important pathways for migration of the Permian and Jurassic oils to the Cretaceous and Neogene reservoirs. The micro-structures and geometric configurations of the unconformity are important for the exploration of petroleum. By analyzing data of cores, logging curves and cuttings logging, three-layer structure of unconformities is identified. Then, further study on the rocks on the unconformity surface, and weathered clay bed and semi-weathered crust of the unconformity surface at Cretaceous bottom is carried out, in which the formation of the unconformity surface and the effects of each layer on hydrocarbon migration are investigated. The formation of the unconformity surface at Cretaceous bottom in the study area is divided into four stages： uplift-weathering period, denudation-transportation period, subsidence-deposition period and diagenetic compac- tion period. The study shows that the rocks above and below weathered clay bed can be effective hydrocarbon migrating pathways, and the weathered clay bed could be local caprock in the area where faults are rare. Oil and gas migrated along the Cretaceous bottom unconformity from south-east to the uplift of Chepaizi.