Research On Suppression Method Of Multiple Reflected Refraction Based On Sources Combination

In the seismic records of low-velocity structures near the surface(such as deserts,loess plateaus,etc.),due to poor excitation conditions of the source,the seismic wave signal will be seriously attenuated during the propagation process,resulting in the development of various secondary interference waves.Among them is a class of shallow-level interference wave——multiple reflected refraction.Because of its high wave velocity and strong energy,it seriously affects the reflection wave of the target layer in the seismic wave field that is close to it,resulting in distortion of the reflection wave shape.It is difficult to suppress the multiple reflected refraction by conventional seismic processing methods alone,multiple reflected refraction greatly affects the correct interpretation of seismic data and brings great difficulties to seismic exploration in low-velocity structure development areas.On the basis of combing the formation mechanism and geological conditions of multiple reflected refraction,the generation mechanism and propagation law of multiple reflected refraction in shallow low-velocity structures are clarified.Based on the mature and complete theoretical study of refraction wave,the dynamics and kinematics characteristics of the multiple reflected refraction are analyzed,and the kinematic time-distance curve equation of the multiple reflected refraction under the excitation depth is derived.Based on the above research,a method of suppressing multiple reflected refraction in the form of source combination in the field acquisition stage of seismic exploration proposed.The method of seismic source combination to suppress multiple reflected refraction includes two aspects.Firstly,clarify the circumstances under which multiple reflected refraction need to be suppressed,and quantitatively give the prerequisites for suppression of multiple reflected refraction.Secondly,under different formation parameters,according to the formula,select the upper and lower limits of the range of source combination parameters to adjust the relative position of the sources.It can suppress the multiple reflected refraction without affecting the reflection wave of the target layer.Several models are established,proper numerical simulation methods is selected for forward simulation,and the source combination test is carried out in the low-speed structural development area of the Loess Plateau,comparing the conventional single shot record with the source combination record.Model verification and practical data application show that the proposed source combination method can suppress the multiple reflected refraction in shallow low-velocity structures to a certain extent,highlight the reflection waves of the target layer,and effectively improve the signal-to-noise ratio and effective wave of the original seismic data accuracy of interpretation.In the near-surface low-velocity structure development area,as a supplement to the conventional excitation mode,it has certain practical significance and helps to refine seismic exploration.