Sedimentary characteristics and favorable oil-bearing facies belts analysis of near-shore subaqueous fan of Nantun formation in Tanan depression

The sedimentary characteristics,distribution,evolution and favorable oil-bearing facies belts of near-shore subaqueous fan of Nantun formation in Tanan depression were studied through the integrated utilization of data of seismology,well-logging and core.The results show that three kinds of sub-facies and four kinds of microfacies can be identified in near-shore subaqueous fan,and the different facies belts show obvious distinctions in sedimentary characteristics.The development of near-shore subaqueous fan concentrated at the downthrown side of the basin controlling fault in the east part of the depression.The overlaying of multistage near-shore subaqueous fan sediments formed two fan aprons which are characterized by and northeast each contiguous,flourish at first while decline at last at the southeast and northeast part of the area.Owning to episodic activities of the basin controlling fault and the distinctions between the sources from southeast and northeast respectively,the southeast fan aprons are a little earlier than the northeast ones in the time of the formation and the decline of the fan aprons.The physical property of braided channels of middle fan sub-facies of near-shore subaqueous fan is the best,and the reservoirs with low-middle permeability developed.The reservoir porosity of different places and burial depths shows a great discrepancy,therefore it is hard that the reservoirs formed a large joint area and high-quality ones.The study area mainly developed lithologic hydrocarbon reservoirs and structural-lithologic composite hydrocarbon reservoirs whose individual scale is small but quantities are numerous.