Sensitivity of interval Vp/Vs analysis of seismic data

Rafael J. Asuaje

Three studies were conducted to evaluate the behavior of Vp/Vs ratio error in beds with different thickness. In the first study, a synthetic model was created to understand how the interval time would affect the calculation of the interval Vp/Vs and an equation was derived to estimate the percent error in the uncertainty of the ratio calculation.

In a second study, the seismic data at Hussar, Alberta showed that Vp/Vs error increased as the analysis time window interval decreased. In addition, the percent error of the Vp/Vs values due to uncertainty was examined and it is suggested to use isochron intervals greater than 150 ms in PP time for robust results. Interval Vp/Vs analysis for data with intervals greater than this isochron have low uncertainty.

In the third study, at Spring Coulee, Alberta, results showed that horizon pick adjustments can reduce error uncertainty by a small factor. In this and the previous studies, it was confirmed that beds with small thickness can have a significant impact on interval Vp/Vs uncertainties, which could lead to erroneous results. Additionally, all studies indicated that interpreters should work with bed intervals greater than 150 ms in PP times and perform horizon adjustments for more precise results.