Poisson's Ratio vs. Compressional To Shear Velocity Ratio (VPVS)
This crossplot displays the relationship between sonic velocities and Poisson's ratio.
Enter sonic compressional and shear slowness values in us/m to see the associated Poisson's ratio. Note that shear slowness should generally be at least 1.60 times greater than compressional slowness. Also note that us/m equals us/ft multiplied by 3.28 ft/m, and that velocity is the reciprocal of slowness.
Velocity ratios can be used as an indicator of lithology. Laboratory analysis of water saturated rocks yields VPVS=1.9 for limestone, VPVS=1.8 for dolostone, VPVS=1.6 in low porosity shaly sandstones, and VPVS=1.8 for clean high porosity sands.
Inputs are highlighted in yellow and outputs are in green. The data point associated with sonic inputs is plotted on the crossplot.
The following lithology based values for Poisson's ratio may be useful:
|hard sandstone||0.18 to 0.22|
|soft sandstone||0.22 to 0.40|
|siltstone||0.20 to 0.28|
|shale||0.30 to 0.40|
Light hydrocarbon decreases the velocity of both compressional and shear sonic waves. However, compressional velocity is affected more than shear velocity, and this means Poisson's ratio will be unrealistically low, if raw data are used to calculate. Data suggest that a Poisson's ratio less than 0.18, or a VPVS ratio less than 1.60 reflects light hydrocarbon effect.
Murphy, W.F., Schwartz, L.M., and Hornby, B., "Interpretation Physics of Vp and Vs in Sedimentary Rocks." SPWLA Thirty-Second Annual Logging Symposium, June 16-19, 1991.