Study On Accurate Correlation Of Tongbomiao And Nantun Formation, South Wuerxun Depression

Wuerxun Depression is one of the secondary tectonic units of Hailaer Basin, which is controlled by Wuxi fault zone. It contains two blocks from north to south and several zones from west to east. The southern block of Wuerxun Depression which is called Wunan Depression is our research area, which included several structural units, such as Wuxi fault terrace zone, Wunan sag, and Bayantala strike-slip structural belt and Wudong slope structural belt. The target zones are Tongbomiao Formation and Nantun Formation, in which we study on fine oil layer correlation.According to the research of core, logging facies and seismic facies, we conclude that depositional systems developed in the target zone are mainly alluvial fan, fan delta, braided delta and lacustrine, based on which and guided by the theory and technology of Sequence Stratigraphy, considering the tectonic evolution and sedimentary evolution, we can identify the critical sequence surfaces and finish third-order sequence division of key exploration wells. Tongbomiao Formation includes sequence SQt and Nantun Formation is consists of sequence SQn1 and SQn2. By the division and correlation of third-order sequence of the sections which control the study area, we can build isochronous third-order sequence framework of the target zone, under which can we analyze changes of the system tracts in those sequences.The division and correlation of oil layer is restricted by third-order sequence framework, based on core descriptions, bore logs and seismic data, using high-accuracy technology of division and correlation of sequence, and referencing the base-level cycle, we can identify high frequency cycle which equivalents to the grade of oil layer, thus finish the division and correlation of the oil layers in Wudong slope structural belt (equivalent to fourth-order sequence). Sequence SQn2 can be divided into oil layer n21 and n22 by MFS F3, while sequence SQn1 can be divided into three oil layers by maximum flooding surfaces of the fourth-order sequences, they are n11, n12 and n13, and sequence SQt contains oil layer t1 and t2, which are separated by F1.Through analyzing the dynamic responses of the stratigraphy and sedimentology which are controlled by the change of A/S, we can identify high-class time surface and establish the division scheme of sublayers of the target zone in Wudong development area, and finally build the correlation framework of sublayers in Wudong oil field.Based on the correlation of the oil layers, we can make isopach maps of those oil layers and research the thickness variation of them, and we can use the technique of palaeogeomorphology reconstruction to analyze the residual thickness, denuded thickness and the characteristics of the palaeogeomorphology during the period of each oil layer in Wunan area.