Sedimentary Characteristics Of Quaternary Shallow Layer And Geological Model Building Of Yihezhuang Area,zhanhua Sag

High precision seismic technique is the most effective way of oil and gas exploration. Exploration practice indicates that the choice of excitation layer in the shallow strata is one of the key factors in determining the quality of seismic signal. Yihezhuang area in Zhanhua sag, is an important oil-producing block in the Shengli Oilfield. Based on the sedimentary theory, the paper combined the theory of geophysical and geotechnical engineering, and took advantage of cores in shallow layers, grain size, heavy mineral, micropaleontology, and cone penetration test(CPT) results. After researching the sedimentary characteristics of the sallow layers of the Quaternary sediments in the research area, geological model of shallow layers has been established and optimum excitation layer has been determined.Sea-level fluctuation and channel migration of the Yellow River affected by climate change are the main factors influencing shallow sedimentary characters. Studies have shown that sediment types of Yihezhuang area are mainly tawny, dark gray silt, argillaceous silt and silty clay, while fine sand and clay is less. Two shell layers develop commonly in the study area. And sediments are rich in mica and carbonate mineral. Five stratigraphic units are divided in the shallow strata, according to sediment characters, microbody paleontological and the shell layer development degree. Corresponding to stratigraphic units; sedimentary evolution after terminal late Pleistocene includes five stages, and they are fluvial facies, tidal flat facies, neritic facies, tidal flat facies, and delta facies.Five sedimentary units get obvious response in the grain size and heave mineral characteristics. Sediments in the bottom fluvial facies and top delta facies are coare, positive skewness, and heavy mineral index shows that it was cold and dry when the two stratas mentioned above deposited. Sediments in the middle marine strata are fine, sorting well, more positive skewness. That indicates that tidal action was main geologic force, while wave action was weak. Heave mineral index shows that it was warm and wet when the marine strata deposited. Heavy mineral combination in the study area is hornblende, epidote, hematite, limonite, garnet, ilmenite, and apatite occurs frequently, which indicated sediments in shallow strata of Yihezhuang area mainly come from the Yellow River system.The key point to study sediments spatial distribution regulation is to realize the quantitative, accurate interpretation of lithology by CPT, and the paper made use of the cross plot of tip resistance(fs) and friction-resistance ration(n) to establish CPT lithology identification chart,and accordingly, made lithologic interpretation of the CPT data in the study area, thus clear the spatial distribution characteristics of the sediments. And lithology model and stratigraphic structure model are built. Combining excitation layer lithology, depth, ghost face, low velocity zone and other influencing factors, the paper determines its selecting principle of Yihezhuang area. Finally, the depth of 12-14 m and 16-18 m formations are selected as the best seismic excitation horizons.