A Dynamic Three-Field Finite Element Model for Wave Propagation in Linear Elastic Porous Media

Abstract

A three-field finite element (FE) model for dynamic porous media considering the de la Cruz and Spanos (dCS) theory is presented. Due to fluid viscous dissipation terms, wave propagation in the dCS theory yields an additional rotational wave compared to Biot (BT) theory. In addition, introducing porosity as a dynamic variable in the dCS model allows solid-fluid nonreciprocal interactions. Due to the volume-averaging technique, the dCS model further accounts for a macroscopic shear modulus and adds a new macroscopic constant. The porous media governing equations are formulated in terms of solid displacement, fluid pressure, and fluid displacement. Space and time convergence rates for the FE dCS model are demonstrated in a one-dimensional case. A dimensionless analysis performed in the dCS framework led to negligible differences between BT and dCS models except when assuming high fluid viscosity. Domains with small characteristic lengths resulted in BT and dCS damping terms in the same order of magnitude. One- and two-dimensional examples showed that dCS nonreciprocal interactions and the macroscopic shear modulus are responsible for modifying wave patterns. A two-dimensional injection well simulation with water and slickwater showed higher wave attenuation for the latter. High frequencies in dCS model were noticed to yield more significant changes in wave patterns. The numerical results highlight the contributions of the dCS porous media model and its importance in simulations of laboratory scale experiments, ultrasonic frequencies, and highly viscous fluids.