Research On Seismic Converted Wave Stacking Method For Ocean Bottom Nodes

The ocean is rich in fossil resource such as natural gas hydrates and petroleum.Seismic exploration,as the most effective means of oil and gas exploration,is naturally also used in marine resource exploration.The geological conditions of China's offshore continental sedimentary basins are complex,and it is difficult to obtain reliable reservoir evaluation and fluid detection results by seismic exploration of offshore streamers.Because the transverse wave cannot propagate in seawater,in order to obtain more abundant longitudinal waves and transforming shear wave information,marine seismic exploration often uses sea surface excitation and submarine receiving(OBN-Ocean Bottoms Nodes)seismic exploration technology,and OBN technology can be used in marine resources.In the exploration and deepsea geological surveys,the technical advantages are taken and the corresponding problems are solved.However,due to the particularity of the observation methods,the methods of converting wave data processing and superposition are different from conventional towline earthquakes.The processes of velocity analysis and motion correction are all performed on CRP gathers or CCP gathers.The key to extracting gathers is to correctly calculate the position of the longitudinal wave reflection point and the position of the converted wave transition point.The land is used to calculate the reflection point.The method of position and transition point position is based on the assumption that the point is located at the same horizontal plane.Therefore,the calculation method of the position of the reflection point and the position of the transition point on the land for extracting the gather is no longer applicable to the OBM seismic exploration data.Processing.Due to the influence of seawater layer,the propagation path of seismic waves is different from that of land,which leads to their time-distance curves are no longer the same,which will also affect the accuracy of velocity analysis and dynamic correction.The process of gather set extraction,velocity analysis and motion correction will affect the profile quality of superimposed imaging.In order to make the superimposed imaging results more accurate,this paper discusses the two locations of the longitudinal wave reflection point of horizontal layered media by using the geometric relationship of OBN observation method.The method is used to analyze the influence of the depth of seawater and the depth of the wave impedance on the position of the reflection point,and the longitudinal wave time-distance curve under the OBN observation system is derived.For the converted wave,the method of calculating the position of the converted point of the land converted wave and the method of calculating the position of the converted point of the OBN are discussed.The influence of the depth of the seawater,the thickness of the formation and the ratio of the longitudinal and transverse wave to the position of the switching point are discussed.The formula of the OBN technology converted wave time interval curve is derived.Then,using the method mentioned in this paper,the trial of the horizontal layered model and the complex model is carried out,and compared with the conventional gather extraction and velocity analysis methods.The results show the position of the reflection point and the transition point calculated by the method mentioned in this paper.More accurate,the velocity analysis results are closer to the superposition speed.The effectiveness of the proposed method is verified by the processing models of the two models.A series of processing processes mentioned in this paper are applied to the processing of OBN data in real ocean,and good results are obtained.