Prestack Vp/Vs scanning and automatic PS-to-PP time mapping using multicomponent seismic data

Osareni Christopher Ogiesoba

ABSTRACT

This thesis discusses the development, testing, and application of prestack methods that scan for the average vertical velocity ratio γ 0 , and the stacking velocities of multicomponent seismic (MCS) data using a converted-wave (PS) non-hyperbolic traveltime equation. The procedure entails computing semblance as a function of two variables namely, the PS velocity Vps and γ 0 , with respect to the PS zero-offset time t ps0 . The results are displayed in 2D and 3D plots. The scanning procedure is tested using numerical data sets and real MCS data sets from the Blackfoot Field in southern Alberta. The algorithms work well with either the shot gathers or the asymptotic conversion point (ACP) gathers. The accuracy increases with increasingly fine sampling of each variable. It is observed that the γ 0 -log from the scanning procedure, agrees very well with the Vp/Vs values from the well log of Well-09-08. In addition, when this γ 0 estimate is used for PS-to-PP time mapping, the time difference between the computed and actual PP time at the target level is found to be 20 ms; being an error of less than 6%.

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