Study Of Early-arrival Velocity Inversion Technology

Seismic velocity is a critical factor in reflecting underground structure and lithology.In the final analysis,geophysical problem is the velocity estimation problem.How to reconstruct the underground velocity field information accurately has become the core issue of seismic exploration and near-surface velocity modeling problem is a important and difficult problem of the common geophysical modeling.The accuracy of near-surface velocity directly influences the results of static correction,velocity analysis and the final imaging in exploration areas.Near-surface modeling methods and technologies commonly used are based on the ray theory of high-frequency approximation,which barely meet the high-accuracy request in current near-surface modeling.So more accurate near surface velocity inversion method is more and more concerned.Full waveform inversion which based on wave equation belongs to nonlinear inversion theory and takes use of seismic full wave field information.In theory,it is regarded as the highest precision modeling method and has achieved the application of the sea real data.As lack of the low frequency information,restricted form land observation system,land serious random disturbance and the influence of near-surface condition,the application of real data in land still exist many difficulties.Based on full waveform inversion theory,this paper jointed the advantage of first-break traveltime tomography and full waveform inversion modeling to introduce the concept of early arrival wave,we introduced a kind of characteristic waveform inversion method-early arrival waveform inversion.Velocity modeling problem is converted into solving the objective function extremum problem,using the best match between observation record and model forward record to rebulid the underground model.We only take use of the early arrival wave information to avoid the disadvantages of shortest path method based on the principle of high frequency assumption in ray theory and the requirement of large offset and low frequency information in the full waveform inversion,we used the kinematics and dynamics of early arrival wave information to fill the "blind area" of conventional modeling means and completed high precision velocity modeling of near surface and shallow.Paper started from the basic theory of waveform inversion,introduced early arrival waveform inversion process.Through model test,it intuitively shows the ability of processing precise velocity modeling,the accuracy and resolution of the inversion results is more higher than traveltime tomography result,the method has the lower nonlinear level and inversion process is relatively stable and high efficiency,convergence effect is relatively good,even in the case of lower initial model precision,it can still distinguish low wave number and high wave number component.Finally,we apply early arrival waveform inversion to land actual data and pay attention to all details of the inversion process.Based on the experience of dealing with model and actual data,the method show the validity,feasibility and practicability We puts forward a set of complex surface velocity modeling strategy aimed at the severe change of lateral velocity and complex surface structure.At the same time,the method combining with other methods of non-seismic method have broad application prospects in mineral reconnaissance,engineering geophysical exploration,oil and gas exploration and other fields...