Sedimentary environment of the Chang 6 oil￣bearing interval of Upper Triassic Yanchang Formation in Jiyuan area,Ordos Basin: Evidences from geochemical data
Wang Teng-Fei1, Jin Zhen-Kui1, Chu Mei-Juan2,3, Li Shi-Xiang2,3, Yu Xiao-Xia1, Wang Xin-Yao1, Li Shuo1
1 College of Geosciences,China University of Petroleum(Beijing),Beijing 102249,China; 2 Exploration and Development Research Institute of PetroChina Changqing Oil Field Company Ltd., Xi'an 710018,China; 3 National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Fields, Xi'an 710018,China
Abstract：The Upper Triassic Yangchang Formation is the main oil-bearing strata in Jiyuan area,middle-western Ordos Basin. The Chang 6 oil￣bearing interval is one of the most important oil-bearing horizons,which can be subdivided into 3 layers,i.e., 63,62,and 61 layers in ascending order. The Chang 6 oil-bearing interval spans two three-order sequences. The redox environment,salinity,water depth and paleoclimate are reconstructed based on element geochemical data. In the warm and humid climate,the lake was generally low in paleo salinity. In addition,both oxidizing and reducing conditions co-existed. The reducing environment gradually decreased and migrated. While the water depth tended to decrease and become stable in the latter. In Jiyuan area,the sedimentary characteristics of Chang 61,62 and 63 layers are different. At the beginning of Chang 6,it inherited the sedimentary characteristics of the lacustrine basin in the end of Chang 7 oil-bearing interval. The lake range of Chang 63 was large and its sand bodies were mainly composed of the mouth bars and distal bars. Turbidite sand bodies developed in semi-deep lake. Along with the declining lake level,the length of the shoreline of Chang 62 was obviously reducing,and the-semi deep lake did not develop. The lake shoreline length of the Chang 61 was slightly smaller than that of the Chang 62,and the sand body thickness increased dramatically. In the range of the lakeshore line,there were many sand bodies formed by superposition of river channels and mouth bars. The results can help to clarify the sedimentary evolution laws of the Jiyuan area and provide reference for further exploration and development.
Wang Teng-Fei,Jin Zhen-Kui,Chu Mei-Juan et al. Sedimentary environment of the Chang 6 oil￣bearing interval of Upper Triassic Yanchang Formation in Jiyuan area,Ordos Basin: Evidences from geochemical data[J]. JOPC, 2019, 21(3): 505-516.
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