THE SQUIRT-FLOW MECHANISM - MACROSCOPIC DESCRIPTION

We introduce a poroelasticity model that incorporates the two most imp ortant mechanisms of solid/fluid interaction in rocks: the Biot mechan ism and the squirt-flow mechanism. This combined Biot/squirt (BISQ) mo del relates compressional velocity and attenuation to the elastic cons tants of the drained skeleton and of the solid phase, porosity, permea bility, saturation, fluid viscosity and compressibility, and the chara cteristic squirt-flow length. Squirt-flow length is a fundamental rock property that does not depend on frequency, fluid viscosity, or compr essibility and is determined experimentally. We find that the viscoela stic response of many sandstones is dominated by the squirt-flow compo nent of the BISQ mechanism and that the viscoelastic properties of the se rocks can be expressed through a single dimensionless parameter ome gaR2/kappa, where omega is angular frequency, R is the characteristic squirt-flow length, and kappa is hydraulic diffusivity. The Biot mecha nism alone does not give an adequate explanation of the observed veloc ity dispersion and attenuation, and the viscoelastic behavior Of many sandstones.