A Finite-Element Procedure to Determine Biots Coefficients of Anisotropic Poroelasticity

Abstract

Numerical rock physics offers an alternative approach to laboratory measurements, being repeatable and essentially free from experimental errors. In this work, we present a set of oscillatory numerical experiments to determine the coefficients of the stress-strain relations of a poroelastic medium saturated by a single fluid. The experiments represent a set of low-frequency (quasi-static) compressibility tests applied to a representative sample of bulk material, where the fluid has enough time to reach pressure equilibration. Each test is associated with a boundary-value problem formulated in the spacefrequency domain and solved with a finite-element procedure. The methodology is used to estimate the poroelasticity coefficients of a homogeneous sample of isotropic Utsira sandstone saturated with either brine or CO2, and the eight coefficients corresponding to a periodic sequence of thin isotropic layers of brine-saturated mudstone and CO2-saturated sandstone. This medium is transversely isotropic in the long-wavelength limit.