THE RELATIONSHIPS BETWEEN THE VELOCITIES, ATTENUATIONS AND PETROPHYSICAL PROPERTIES OF RESERVOIR SEDIMENTARY-ROCKS

We have measured the velocities and attenuations of compressional and shear waves in 29 water-saturated samples of sandstones and shales at a confining pressure of 60 MPa and at frequencies of about 0.85 MHz. T he measurements were made using a pulse echo method in which the sampl es (diameter 5 cm, length 1.5 cm to 2.5 cm) were placed between perspe x buffer rods inside a high-pressure cell. The velocity of each seismi c wave was determined from the traveltime difference of equivalent pha se points (corrected for diffraction effects) of the signals reflected from the top and from the base of each sample. Attenuation was determ ined in a similar way by comparison of the diffraction corrected ampli tudes of the signals. The attenuation data are presented as 'quality f actors': and Q(p) and Q(s), for compressional and shear waves respecti vely. The results show that Q(s), is strongly correlated with V-s, tha t Q(p), is weakly correlated with V-p, and that Q(p), is strongly corr elated with Q(s). Q(p) is strongly dependent on the volume percentage of the assemblage of intra-pore minerals, whether they are clays or ca rbonates. It is concluded that the attenuation mechanism is due to the local fluid flow arising from the differential dilation of the solid rock frame and the intra-pore mineral assemblage, which is a result of their very different elastic moduli.