Laboratory‐based seismic attenuation in Fontainebleau sandstone: Evidence of squirt flow

Abstract

AbstractAt seismic frequencies (1–100 Hz), we studied attenuation in the laboratory using the forced oscillation method. We adopted the longitudinal mode of oscillation, which yields the Young's modulus and the corresponding attenuation, here defined as the inverse quality factor. A Fontainebleau sandstone with a porosity of 8% and a permeability of 12 mD was saturated with different fluids and investigated at the confining pressures of 5, 10, and 15 MPa. At all the measured confining pressures, while attenuation was zero for the dry sample, for partial and full water saturation, it gradually increased from nearly zero to ~0.02 with increasing frequency. The sample was then fully saturated with glycerin‐water mixtures of varying viscosities, up to that of glycerin (8, 92, 485, and 1414 cP). At the confining pressure of 5 MPa, a bell‐shaped attenuation curve peaking at ~6 Hz with a magnitude of ~0.11 was observed when the sample was fully saturated with glycerin (1414 cP). A decrease in viscosity of the saturating fluid shifted the attenuation curve to higher frequencies, and an increase in confining pressure caused a decrease in the overall magnitude of attenuation. The data obtained for glycerin were compared to a simple squirt flow model with sufficient agreement, implying that squirt flow is the dominant mechanism responsible for the observed attenuation.