Validating the theoretical model for squirt-flow attenuation in fluid saturated porous rocks based on the dual porosity concept

Pressure dependency of seismic properties of porous rocks is important for a range of geophysical applications. Recently, a theoretical model has been developed to interpret the pressure and frequency dependent squirt-flow attenuation in fluid saturated porous rocks based on the dual porosity concept. We implemented laboratory measurements of dry rock porosity and ultrasonic (compressional and shear wave) velocity and saturated rock velocity and attenuation on two sandstone samples with varying confining pressures from 5 to 60 MPa to test the pressure dependent attenuation of the squirt-flow model. Based on the experimental data, the pressure dependent compliant and stiff porosity were obtained by fitting the dual porosity model to the measured variation of total porosity with pressure, and the compliant pore aspect ratio was estimated as a free parameter to make the model predicted velocity of the saturated rocks best fit their laboratory data. Comparison of the modelled attenuation with the measured variation of attenuation with pressure showed that the squirt-flow attenuation is consistent with the measurement at low-pressure regime but underestimates the experimental data when the confining pressure becomes higher. The results confirm the validation of the squirt-flow model to explain the attenuation at low pressures and suggest the requirement of the combination with other theoretical models to fully interpret the attenuation at high confining pressures.