The Use Of Joint Interpretation In Yabei Sag And Improvement Of Magnetic Diurnal Variation Correction

The seismic exploration method has a high resolution in detecting layered medium and is widely used in marine geophysics exploration. However, when facing the complex geological circumstance in unexploited zo ne, the seismic exploration method has many defects such as its weak capability in detecting the interference of the multiple wave of shallow layer and the shielding effect of the shallow layer with strong reflection characteristic. Using single seismic me thods may not lead to a well interpretation in nowadays marine geophysics research. The marine gravity and marine magnet research has a high lateral resolution and has a relatively cheap price. So it could be a good supplement of seismic exploration in ocean area.Under the information of geological background information, the author used the jointed interpretation method of marine gravity and magnetic data of two survey lines in Yabei Sag, which in the north part of Qiongdongnan Basin. Under the restriction of the seismic section and drilling information, we made a 2.5D initial model based on the Encom Model Vision interpretation software to conduct the inversion. The result shows that the deposition substrate of Pre Cenozoic group has the density of 2.70 g/cm3, and the density of sedimentary strata varies from 2.18g/cm3 to 2.51g/cm3. Under the inversion calculation, the geological anomalies at 1200 m depth reveals to be the igneous diaper of low density and medium susceptibility which form in the late Neogene. And by analysis of magnetic data, there would be large area of igneous intrusions. As the related volcanic plays as a dual role of construction and destruction in the formation and accumulation of oil and gas, it should be considered in the future research of Yabei Sag.When we conduct the geomagnetic diurnal variation of the magnetic acquisition in this research, we found there is obvious time shift and amplitude changes between the geomagnetic diurnal variation data we collected in the base station in land and in the survey zone, which we defined those time shift and amplitude change as residual time difference and amplitude difference. Based on the massive data analysis of the residual time difference and amplitude difference of geomagnetic diurnal va riation data from 15 survey zone in the offshore survey area in China, we found the residual time difference exists in nearly all survey zone. And we generate regular patterns of the time shift and amplitude change with their influential factors and suggest a correct method of nowadays geomagnetic diurnal variation of marine magnetic survey.