Anisotropic Poroelasticity – Does it apply to shale?

Shale plays an important role as cap rock above oil and gas reservoirs and above e.g. CO₂ storage sites, as well as being source and reservoir rock in development of so-called unconventional reserves. Shale anisotropy needs to be accounted for in geophysical as well as geomechanical applications. This paper presents a brief description of anisotropic poroelasticity theory, and compares it to its more familiar isotropic counterpart. Experiments performed with field shales are presented, and the static mechanical behavior in terms of drained versus undrained moduli, Skempton parameters and Biot coefficients are shown to be consistent with the poroelastic approach. The necessary steps to provide static properties from seismic data and further link these measurements to laboratory ultrasonic data are briefly discussed.