Frequency dependent elastic properties and attenuation in heavy-oil sands: comparison between mea- sured and modeled data

We have measured elastic (bulk and shear modulus) and acoustic (compressional and shear wave velocities) properties of heavy-oil sands over a range of frequencies (2− 2000Hz) covering the seismic bandwidth and at ultrasonic frequencies (0.8MHz). The measurements were carried on heavy-oil sand sample from Asphalt Ridge, Utah at a constant temperature ( 20oC) and different confining pressures using the low frequency experimental setup at Colorado School of Mines. Four different modes of intrinsic attenuation, extensional (QE), shear-wave (QS), compressional-wave (QP) and bulk compressibility (QK) were estimated. Both compressional and shear wave velocities show significant dispersion probably due to both the the inherent viscoelastic property of heavy oil and viscoelasticity arising due to oil and sand interactions. The measured attenuation (Q−1) values are significantly high indicating significant loss of energy during wave propagation. We made an attempt to model the measured acoustic properties using effective medium theories. The results show reasonably good agreement between the measured data and modeled response especially at non-zero confining pressures. The measured attenuations were modeled using the Cole-Cole model.