| The oil &gas exploration in the east of China have been in the the mid and late stage. subtle-trap exploration have become the front theme. The beach and bar which formed in the gentle nearshore slop get the high opinion of geologists in china. But some problem restraint the exploration in beach and bar. For example, the single sand body with thin thickness always multilayer overriding in vertical direction and aeolotropism in horizon. Many control factor limit its distribution and oiliness character.Dawangbei sag located in the center of Chenzhen depression. extended in EW. Complex faulting systems develop in it, and which form many structural nose zones. When the Second member of Shahejie formation deposited, in which basin is in the post-rift period, Dawangbei sag has the configuration that was faulted in the north and onlapped in the south. Based on the theory of high-resolution sequence stratigraphy, the Second member of Shahejie formation is divided into one 3rd order sequences, two 4rd order sequences and six 5rd order sequences.The Second member of Shahejie formation developed many types of sedimentary facies, that is, fluvial-floodplain, slumping turbidite fan, offshore-shallow lake, beach and bar, braided-river delta and fan delta. The small fan delta and delta only developed in the south of sag, which near the Chennan fault. The distribution of beach and bar is regularity, which was controlled by the palaeotopography, provenance and the development of the delta, fan delta which accompany with it. The bar distributed in banded along the lakeshore and around in the front of delta, or at the rim of palaeohigh. The bank distributed in sill-like near the lakeshore or the rim of bar and delta. The bar and the bank could differ in their lithology, electrical property and seismic reflection character. Based on the analysis of depositional model of Second member of Shahejie formation and research of control factor of distribution of the beach and bar, it can be inferred that the distribution of the beach and bar was controlled by the distribution of hydropower energy balance zone, the character and direction of provenance, the configuration of the basin. The beach and bar usually developed below the regional unconformity in the post-rift period, and frequency extension and shrink of lake basin is favour of its development. It has the inter inhibitive relationship with the delta which developed around. In the research of its distribution, the technology of palaeogeomorphological and palaeobathymetric recovery could be the important reference.Based on the analysis of test data, the reservoir in research zone is mainly mesoporosity and low or extremely low permeable. The bar has the better porosity, permeability and lubricity than the band. The reservoir of the beach and bar in the south gentle slope have the best porosity and permeability, but lack of oil sources, its show of gas and oil is not very good. The reservoir of the beach and bar near well Da55 located in the center is mainly siltstone, which link up with source rock by Da1 fault, its show of gas and oil is better; the reservoir near well Da65 which located in the north shows good porosity and permeability, but its connectedness should be researched further.Combined with the analysis of known pool and the oil-showed well, based on the research of distribution of depositional system and reservoir character of the beach and bar, the favorable zones are pointed out. Also combined with the condition of structure and resource rock ,the favorable play for exploration have been forecasted. |
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