Publication History: This article was written especially for "Crain's Petrophysical Handbook" by E. R. Crain, P.Eng in 2015. This webpage version is the copyrighted intellectual property of the author.

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Lithology From Vp/Vs Velocity Ratios
The dipole shear sonic log provides compressional and shear travel time values that can be used for quicklook lithology estimation, based on the compressional to shera velocity ratio (Vp/Vs) -- see graph shown below.   It is probably not accurate enough for quantitative log analysis purpses. Vp/Vs is relatively independent of porosity but may have some gas effect

When recorded especially for the purpose, seismic data can be inverted to provide compressional, shear, Vp/Vs ratio, and Poisson's ratio seismic sections. The Vp/Vs ratio inversion can be interpreted for litholgy using the same quicklook rules shown below.  Values lower than those for the expected lithology may indicate gas or inadequate inversion processing.
      1: Vp/Vs = DTS  / DTC


RECOMMENDED PARAMETERS:

Sandstone Vp/Vs = 1.55 1.70, normally near 1.60

Dolostone Vp/Vs  = 1.65 1.80, normally near 1.70

Limestone Vp/Vs  = 1.80 1.90, , normally near 1.80
Anhydrite and Shale Vp/Vs = 1.90 - 2.00, , normally near 1.95

 

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