The Study On Sedimentary Facies Of Chang 6 Oil Formation In Zhengning-Yijun Area

Chang 6 oil-bearing formation in Zheng Ni-Yi Jun area is rich in oil resources, but the contradiction of deep exploration degree and low geological study is increasingly obvious.Sedimentary facies and sand body distribution is still controversial. The further exploration of oil and gas becomes difficult. Based on sedimentary principle and integrated use of the theory and methods of sedimentary petrology,petroleum geology, logging geology, through a comprehensive analysis of the outcrop,drill core data and logging data, the paper studies the source direction,sedimentary facies types and distribution of sedimentary faeies of Chang-6 oil formation of the Triassic Yanchang Formation of Zhengning-Yijun area of Ordos Basin.To classification and correlate the stratum, through the way of flag layer control and cycle contrast, combined with the thickness principle, we divide Chang-6 oil formation into Chang61、Chang 62 and Chang 63 in study area. The top layer structure is presented the characteristics of high-southeast and low-northwest, developes three-four nose-like structure from northwest to southeast.Through the study of paleocurrent direction, light and heavy minerals,rock debris analysis,as well as ancient land distribution feature,we think the study area mainly affected by the northeast and southwest provenance, and locally influenced by the south provenance. We speculate that northeast provenance was from archaeozoic metamorphite of Yinshan Mountains and Daqingshan Mountains, southeast provenance was from Longxi old land and south provenance was from Qinling orogenic belt.According to core description,outcrop, combining with the rock type, depositional texture,structure characteristics and paleontologic, we identified that Chang-6 developed delta-lacustrine-gravity flow sedimentary systems in study area.For the first time,sandy debris flow are identified.The bottom die structure,defomation structure, tear shaped boulder clay tablets and bouma sequence are widely developed in the study area. To the further study,facies can be divided into four types of sub-facies including sandy debris flow, turbidity current,deep lake and delta-front, which can be further divided into seven categories of micro-phase.Through single well facies analysis and connecting-well sections comparison,we draw the distribution fig of sedimentary facies and sand body in different period.The distribution rule of sandbodies is determined by sedimentary facies. Sedimentary environment of Chang61、Chang62、Chang63 subages have good inheritance, which make all the sandbodies of different time spreading in the northeast-southwest direction.The scale of sandbodies gradually become smaller from Chang63 to Chang61.