Orientation Study Of Ocean Bottom Node Seismic Three-Component Geophone Based On Direct Wave Polarization Analysis

In OBN acquisition,due to its geophone in direct contact with the seabed,therefore,relative to conventional offshore streamer seismic exploration technology,OBN seismic data containing a large number of P-wave information,but also contains a wealth of information converted wave.Thanks to its unique acquisition method and the omnidirectional P-wave and converted shear wave information obtained through processing,it can play an outstanding role in oil and gas exploration at the bottom of the ocean and structural investigation of deep seabed.However,in the real data collection process,the geophone placed on the seabed are often affected by factors such as seafloor fluctuations and ocean currents.It is often difficult to ensure that each three-component geophone is completely placed according to requirements,That is to say,the x component of the three-component geophone is not parallel to the Inline direction of observation geometry system design,the y component is not perpendicular to the Inline direction,and the z component is not in the vertical state.In response to this problem,if a threecomponent geophone equipped with a gimbal is used,the vertical component of the threecomponent geophone can be adjusted to the vertical state by using the direction mark and the leveling bubble on the three-component geophone during the acquisition process.The x component is parallel to the line direction of the observing system design.If the threecomponent geophone is not equipped with a gimbal,orienting a three-component geophone using seismic data acquired by OBN.According to the theory of elastic wave,in the case of isotropic homogeneous medium,the polarization direction of the direct P-wave is in line with its propagation direction.Therefore,this paper mainly uses the polarization information of the direct wave to correct the three-component geophone.In this paper,the structure of OBN instrument and its acquisition method are briefly introduced,and the coordinate rotation is realized by right-handed coordinate system and Euler rotation transformation.Under the condition of isotropic homogeneous medium,the polarization characteristics of different types of seismic waves are analyzed by theoretical model data.From the analysis results,although the vibration modes of P wave and SV wave are different in the plane where the inspection connection line is located,P wave,SV waves all have linear polarization characteristics.Then it analyzed under different formation conditions velocity model,a direct difference in the polarization direction of the P-wave propagation direction thereto,to provide a reference for the subsequent use of the direct wave polarization direction oriented three-component geophone.In the aspect of three-component geophone orientation,it is mainly divided into two cases.The first one assumes that the horizontal component is corrected under the vertical condition of the Z component.In the horizontal component correction process,the X component can be corrected to the direction of the design line,Y component is corrected to the direction of the vertical line.It is also possible to correct the X component to the radial direction and the Y component to the tangential direction.The second hypothesis that the Z component deviates from the vertical state,the polarization analysis of the corresponding two components of the first arrival wave is sequentially obtained to obtain three Euler rotation angles,and the Z component is corrected to the vertical direction by Euler rotation,and the X component is corrected.To design the line direction or radial direction.This paper mainly aims to orient the three-component geophone based on the polarization characteristics of seismic waves.This method needs to pick up the arrival time of the direct wave,and it is affected by the initial arrival time window size,interference signal and anisotropy condition in the calculation process,but for the seismic data without the threecomponent geophone orientation,the method can play an important role.In the paper,the correction of theoretical model data and real seismic records shows that the method has a good application effect.