An experimental study of modulus dispersion and attenuation in sandstones at seismic frequencies

Abstract

We present the results of our measurements conducted on two Donnybrook (A and B)and one Harvey (C)sandstone samples with high (590 mD) and low (7.8 mD and 9.6 mD) permeability. There were no significant attenuation and dispersion observed in the high-permeability sample A. Two distinct interrelated effects have been indicated in the water/brine saturated low-permeability samples B and C. Prominent peaks of extensional attenuation were found at frequency of 0.8 Hz in sample B and at frequencies ~7 Hz (at effective pressure of 23 MPa) and ~20 Hz (at effective pressure of 9 MPa) in sample C. The dispersion of the bulk moduli of both samples in the frequency range from 0.1 to 100 Hz was also detected. The dispersion of the bulk and shear moduli of the samples in the dry state was within the accuracy of our measurements. Our results demonstrate that the low frequency limit of acoustic dispersion for low-permeability rocks can correspond to seismic or even teleseismic frequency band.