The Researches On Improving The Precision Of The Converted Wave Velocity Analysis

With the development of lithological exploration,the P-wave and S-wave jointexploration attracts more and more people’s attention.Compared to the sole P-waveexploration,the P-SV converted wave exploration is easy and feasible and has the lowcost. Converted wave data can provide more extensive information on undergroundrock,these information play an important role at lithology inversion,fracturedparameters extraction and gas detection.Now P-SV converted wave exploration hasbecome the main means of S-wave exploration,particularly along with themulti-component submarine cable technology s use,the processing of converted waveis gradually developed to the conventional production and is becoming a new hot spotin Geophysical field.In seismic exploration,high resolution seismic data processing has been widelyused,along with the high request of exploration precision.But in the processing of highresolution seismic data,high resolution stack velocity analysis is one of the importantlinks.In converted wave data processing,velocity parameter is most important andmost difficult to grasp.Therefore,how to seek the exact and reasonable velocity is thekey point in the entire converted wave processing.In particular,after picking up thehigh-precision,how to pick up the exact S-wave velocity parameter is becoming amajor challenge in converted wave data processing.Because of the ray asymmetry of the down going and upgoing waves,the velocityanalysis based on the CMP gather cannot be adapted to that of the convertedwave(CCP). Main difficulties are from special characteristics of the CCP bin and CCPtime-distance relation. For one thing,even if we assume that the reflection layer ishomogeneous and horizontal,the position of the common converting reflection pointwill be changed with the offset,the depth of reflection layer and ratio of the S to Pwave velocity. For another, the time-distance relation to make out velocity analysis,wecannot get the correct value of S-wave velocity,especially with the shallow-middleevents or large offsets. On the other hand,if we analyze the velocities using all tracestraditionally,the resolution of velocity spectra will decrease greatly when one wishesto distinguish between neighboring primary events from reflectors with conflicting dip,or to identify primaries in the presence of multiples.Based on the previous work,by analyzing,researching and concluding the problemsabove,this thesis has finished the following researches.Firstly,analyzed the CCPtraveling characteristics,factors and computation formulas,the method of CCPgathering bin has been realized.Secondly,the traditional velocity analysis is made outwith CCP time-distance relation and the formulas of CCP computing.Thirdly,based onthe traditional velocity analysis,a so-called velocity analysis of covariance which canimprove the resolution of velocity spectra greatly,has been systematically studied andaccomplished.At last,three methods above were cheeked and compared withtheoretical and practical data.Conclusively,it is shown that the velocity analysis ofcovariance is a highly accurate method of the high resolution.