Sensitivity of interval Vp/Vs analysis of seismic data

Rafael Asuaje and Don C. Lawton


The ratio of a compressional P wave to a shear S wave is of great importance for converted PS wave applications. Dipole sonic logs can provide accurate velocity ratio calculations but are restricted to the location of the corresponding well. Isochrons from interpreted horizons on seismic data can provide information on Vp/Vs throughout the volume that can be used for lithology and fluids studies about a particular formation. Proper interpretations of these events are necessary to avoid erroneous results. The objective of this paper is to set guidelines for an interpreter to accurately pick events and understand the error that can be expected from various isochron intervals to ultimately suggest a minimum interval time that can provide accurate Vp/Vs values.

In a study on the Hussar data set, based on the increasing observable error with respect to decrease in the time intervals, as well as taking into consideration the variability of the Vp/Vs values due to uncertainty it is suggested to use isochron intervals greater than 150ms. Interval Vp/Vs analysis for data with intervals greater than this time presented low uncertainty.

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