Pore Pressure Prediction From S-wave, C-wave, And P-wave Velocities Available to Purchase

The Eaton method for predicting pore pressures from Pwave velocities can be easily extended to S-wave and Cwave velocities, as validated by numerical modeling using well-known rock physics relations. Although originally described using an exponent of 3 (velocity ratio cubed equals the ratio of effective stresses), we show that P-wave pressure prediction using Eaton can require exponents anywhere from 3 to 5, with the exponent generally increasing with depth. S-wave velocities, being more sensitive to changes in effective stress, require a smaller exponent, generally about 2, although this is also a function of depth. We demonstrate the validity of this smaller exponent with an example of pressure calculation using actual shear velocities from a dipole sonic, with corroborating MDT pressure measurements. C-wave velocities possess pressure sensitivities intermediate between S-waves and P-waves, and hence require an exponent intermediate between the two, or about 2.5.