Research On VSP Converted-wave Separation And Seismic Imaging Method

Compared with conventional seismic,Vertical Seismic Profiling(VSP)is expert in recognition ability,high exploration precision and imaging result.It can clearly display the geological structure and petrophysical properties near the well,which is complementary with conventional seismic data.VSP has gradually become a powerful technology for solving underground structure imaging and oil and gas reservoir description in exploration.Therefore,it is necessary to carry out research on VSP data processing methods.At present,VSP exploration mainly uses primary wave source,and a large number of converted shear waves will be generated during the propagation.If the converted shear wave can be fully utilized to imaging,the imaging of the underground structure will inevitably improve the accuracy of VSP exploration,so this paper aims at the processing and application of shear waves from VSP data.This paper focuses on two main steps of transforming shear wave extraction and imaging in VSP data processing.Firstly,the VSP wave field is forwarded by the second-order,spatial2L-order staggered grid finite difference method of wave equation.The artificial boundary reflection is attenuated by the perfect matching layer(PML)absorption condition.For the VSP wave field we obtained,analyzing the characteristics about the main wave especially converted wave.Subsequently,extracting the converted wave by characteristic difference between the longitudinal and transverse waves based on the high-resolution Radon transform.Based on the optimization of the filtering,an angle filtering method which is based on the difference of the longitudinal and transverse wave propagation angles is proposed to enhance the accuracy of the converted wave extraction.Finally,researching on the application of the reverse time migration imaging technique in VSP data,which includes the principle of reverse time,normalized crosscorrelation imaging conditions and the Laplace filtering for low-frequency noise suppressing to improve the imaging accuracy.The model and actual data processing results show that the VSP converted wave extraction and reverse time migration imaging techniques used in this paper can restore the real condition of the underground structure well,and the imaging results have higher resolution and signal-tonoise ratio.