Sedimentary facies and its evolution of the Chang 9 interval of Upper Triassic Yanchang Formation in Ordos Basin
Fu Jinhua1,2,3, Li Shixiang2,3, Liu Xianyang2,3, Deng Xiuqin2,3
1 PetroChina Changqing Oilfield Company，Xi′an 710018，Shaanxi 2 Research Institute of Exploration and Development，PetroChina Changqing Oilfield Company，Xi′an 710018，Shaanxi 3 National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Fields，Xi′an 710018，Shaanxi
Abstract：Delta and lacustrine sedimentary facies are recognized from the Chang 9 interval of the Upper Triassic Yanchang Formation in the Ordos Basin.The deltaic plain distributaries channel sandbodies and deltaic front subaqueous distributaries channel sandbodies are high quality reservoirs.Based on the research of sedimentary facies，according to the single factor analysis and multifactor comprehensive mapping method，the sedimentary facies distribution of the upper and lower parts of Chang 9 interval of Yanchang Formation in the Ordos Basin were studied and mapped.The single factors include strata thickness，content of deep water sedimentary rocks，sandstone thickness，sandstone strata thickness ratio，authigenic chlorite development characteristics，paleontology characteristics，sedimentary structure combination characteristics.Discussion was made about the sedimentary evolution rule of the Chang 9 interval.The results show that the Chang 9 interval of Yanchang Formation was characterized by the deposition of multiple delta sedimentary system which surround the lake and have multiple water systems and multiple provenances.The meandering fluvial deltas were mainly developed in the northeastern Ordos Basin，and the braided fluvial deltas were mainly developed in the western Ordos Basin.The deltaic plain distributaries channel microfacies and deltaic front subaqueous distributaries channel microfacies were well developed.During the depositional period of the lower part of Chang 9 of Yanchang Formation，semi-deep custrine was only developed in the center of the Ordos Basin.During the depositional period of the upper part of Chang 9 interval of Yanchang Formation，the custrine basin began to expanded，lake shoreline moved to the land，lake area enlarged，and the semi-deep custrine deposition greatly developed.From the lower part to the upper part of Chang 9 interval of Yanchang Formation，the water depth changed from shallow to deep.Correspondingly，a set of oil shale with hydrocarbon generating potential are deposited in the study area.
Fu Jinhua,Li Shixiang,Liu Xianyang et al. Sedimentary facies and its evolution of the Chang 9 interval of Upper Triassic Yanchang Formation in Ordos Basin[J]. JOPC, 2012, 14(3): 269-284.
