Study On Elastic Seismic Wave Full-traveltime Inversion Method

As the improvement of computer capabilities and inversion theory,the traveltime inversion method based on the elastic wave equation organically integrates the iterative inversion theory and the conventional migration velocity analysis,providing reliable velocity data for the pre-stack depth deviation,migration,lithology judgment and hydrocarbon reservoir identification through an automatic iteration process.It can also provide an initial velocity model that can accurately describe kinematic information for full waveform inversion under wave equation theory.This method has gradually attracted more and more attention of geophysical researchers and become one of the research hotspots in the field of exploration geophysics.With the introduction of seismic wave inversion theory,the traveltime inversion method of data domain and imaging domain is be analyzed,and the full-traveltime inversion method is extended from acoustic wave media to elastic media.Focusing on elastic wave specialty,the elastic wave full-traveltime inversion method is realized.Based on the data domain traveltime inversion theory,in order to take into account the specificity of elastic multi-component seismic data and the simplicity of calculation of travel time residuals,multicomponent data is utilized as a vector to perform cross-correlation calculation,calculating the traveltime residuals.The simultaneous inclusion of P-wave and S-wave velocity errors helps to increase the inversion accuracy of velocity.Aiming at the Born gradient and traveltime gradient,a simple model test under different background speed conditions indicates that the traveltime gradient has obvious advantages compared to the Born gradient while the initial model is far away from the real velocity model.Compared with the traveltime inversion of the data domain,the extension of the full-traveltime inversion of the elastic wave of imaging domain calculates the vector wave field as a vector to perform the dot product cross-correlation,and it is essential to select an appropriate parameter disturbance item,producing reflected wavefield data during the migration/de-migration process,which in turn forms tomographic components during gradient construction and updates low-wavenumber information.In this paper,the initial model is used to calculate the Lame constant gradient generated by the gradient as a disturbance term to generate a multi-component reflection wave field,effectively recovering the low-wave velocity information in the middle and deep layers.Finally,both the numerical tests of the simple multi-layered geological model and the partial Sigsbee2 A model indicate the effectiveness and stability of the theoretical method and the algorithm.