Research And Application Of RVSP Bispectrum Analysis Method Based On Anisotropy Theory

RVSP(Reverse vertical seismic profile)and VSP(Vertical seismic profile)are two important borehole seismic exploration methods for fine detection of complex underground structures.Among them,RVSP adopts the observation system of in-well excitation and ground reception,which is easier to carry out large-scale ground geophone layout and has higher data acquisition efficiency.In recent years,with the breakthrough of borehole excitation problem,RVSP exploration method has been widely used in solid mineral resources,shallow geothermal geological structure and coal mine water channel detection at home and abroad.However,compared with ground earthquakes,in the same range of ground receiving arrangement,because RVSP uses borehole excitation,the incident angle of reflected wave is larger,which leads to the prominent problem of large offset(offset)reflection wave correction tensile distortion,which limits the effective application of large offset data and affects the advantages of high efficiency of RVSP data acquisition.Therefore,in view of the above problems,based on the theory of anisotropic media,this thesis focuses on the following three aspects :(1)The control effect of anisotropic Thomsen parameters on group phase velocity is analyzed in detail.The time-distance curve equation of RVSP reflected wave in VTI medium is derived,and the influence of offset on the travel time of RVSP reflected wave is discussed and summarized.(2)Based on the VTI medium theory,the velocity analysis and NMO correction method based on RVSP common-shot gather are studied.(3)By establishing numerical models of different media and structures,the RVSP data analysis method under anisotropic theory is simulated and studied,and the actual data are analyzed and imaged.Through theoretical analysis,numerical simulation and practical data application verification,this thesis mainly achieved the following results and conclusions :(1)The time-distance curve equations of RVSP direct wave and reflected wave based on VTI medium theory are derived.The theoretical analysis shows that under the same offset condition,the travel time of RVSP reflected wave based on anisotropic theory is closer to the actual travel time of reflected wave,which lays a theoretical foundation for the dynamic correction of RVSP reflected wave time-distance curve equation based on anisotropic theory.(2)RVSP bispectrum analysis method based on VTI medium theory is proposed.According to the time-distance curve equation of anisotropic RVSP direct wave and reflected wave,the bispectrum(velocity spectrum + anisotropic parameter Eta spectrum)analysis algorithm flow of direct wave and reflected wave based on RVSP common shot gather is constructed,and the corresponding analysis software module is developed based on matalb appdesigner.(3)Numerical simulation studies show that RVSP bispectrum analysis has good applicability for different media and different structural model conditions.In this thesis,four kinds of models are established,including two-layer layered anisotropic medium model,multi-layer layered isotropic medium model,multi-coal seam with overlying goaf model and inclined layered isotropic medium model.The theoretical seismic data under RVSP observation system are simulated by using wave equation and ray tracing forward modeling method.The bispectrum analysis method proposed in this thesis can improve the dynamic correction effect of large offset data,and has obvious effect on expanding imaging range and imaging quality.(4)Finally,through the application analysis of the actual data of coalfield RVSP,the occurrence state of multiple thin coal seams and the occurrence characteristics of small faults are described by using the bispectrum analysis method.