Velocity Analysis Of Converted Wave With AVO Effect

Converted wave velocity analysis is a key step in converted wave seismic dataprocessing, which directly affects the precision of the stacked profile. Because thepropagation paths of the converted wave are asymmetric, the converted point positionis no longer the common reflection point position, and extracting traces method ofconventional p-wave cannot be applied to converted wave data. The conventionalhyperbolic approximation method also cannot reflect the real converted wavepropagation characteristics. The time-distance curve of converted wave is elliptic type,so the conventional p-wave velocity analysis method cannot be used in convertedwave velocity analysis. In field seismic data, amplitude changes with the offsetdistance, even polarity reversal happens, so it is necessary to take AVO effect intoaccount to obtain a high precision velocity.P-wave velocity analysis methods have been mature, conventional velocityanalysis methods includes stack energy method, similar coefficient method andrelated methods etc. In this thesis, improved AB semblance coefficient method iscompared with the conventional method in theory model for time resolution, velocityresolution, signal-to-noise ratio, velocity scanning interval, window size of thescanning, spread length etc, especially seismic records with AVO effect. The precisionof stack energy method is low when seismic event is approximate or coherent.Although related methods and semblance coefficient method have high precision,when there is AVO effect, energy cannot be concentrated and high precision velocityspectrum cannot be obtained. AB semblance coefficient method has higher precisionin time resolution, velocity resolution, signal-to-noise ratio, velocity sampling interval,near and far offset distance, etc, especially for seismic records with AVO effect, betterenergy spectrum can be obtained.For converted wave velocity analysis, I analyzed and summarized the key issuesin the converted wave velocity analysis, the calculation method of converted pointposition are compared, methods of calculating time-distance curve of the convertedwave are summarized, and the precision of each method is compared. The exactsolution of the converted point position and double square root of the non-hyperbolictime-distance equation are adopted in converted wave velocity analysis in this thesis.Converted wave velocity analysis has been a key technique in converted wave data processing. Converted wave velocity analysis method is studied in this thesis andgeneral workflow of the converted wave velocity analysis and some difficulties aresummarized, especially the studies on the converted wave velocity scanning withAVO effect. Semblance coefficient method has been a common velocity analysismethod, however, when there is AVO effect, especially for polarity reversal, theprecision of this method will be greatly reduced. In this thesis, based on the ABsemblance coefficient method of PP wave, AB semblance coefficient method ofconverted wave is developed to solve the velocity analysis of converted waves withAVO anomaly. Theoretical models are tested and analyzed and show that this methodcan reduce the AVO effect of converted wave. The results demonstrate that ABsemblance coefficient velocity analysis method can be used to more common seismicdata and improve the precision of the converted wave velocity analysis.