Elastic wave velocities in sedimentary rocks

Abstract

From a study of the transmission of dilatational pulses through rods it has Seen found possible to calculate not only the dilatational velocity but also the rotational (shear) velocity. From these velocities the elastic moduli of isotropic materials can he computed. The results are insensitive to boundary conditions and hence the method can be used when the material is surrounded by oil in a pressure chamber. The velocities in sedimentary rocks have been measured in the ranges 0–1100 kg/cm 2 and 25–175°C. In addition, one limestone and one dolomite have been measured up to 2000 kg/cm 2 . The dilatational and rotational velocities and the elastic moduli as a function of pressure and temperature are presented for selected samples. A comparison of our results with those obtained by other methods is given. Although our measurements are based on pulses which have an equivalent frequency of 2.0–6.0 megacycles, there is no apparent discrepancy with low‐frequency and static measurements. This would indicate that, at least for the rocks for which a comparison can be made, dispersion is not important. The elastic moduli are computed as functions of depth with an assumed gradient of 9.5°C per 1000 ft. Values of Poisson's ratio are constant or increase slightly with pressure over the experimental range.