Stochastic depth conversion requires by a number of a priori choices: choice of the appropriate velocity laws; choice of appropriate variogram models to characterize time picking uncertainty; and choice of appropriate variogram models to characterize residual variations around the velocity law.  

To validate the choice of velocity model, it is useful to compare statistics on well depth residuals before and after kriging estimation (please see figure a) and refer to cross-plots of actual well depth versus estimated depth using average velocity law (please see figure b).