Poroelastic Response of a Fractured Rock to Hydrostatic Pressure Oscillations

Abstract

Poroelastic coupling between fractures and the surrounding rock is important to numerous applications in geosciences. We measure the in-situ fluid pressure and local strain response of a fractured carbonate sample to hydrostatic pressure oscillations. A linear poroelastic model that represents the rock sample is parameterized using X-ray imaging and ultrasonic wave transmission measurements. The numerical solution, based on Biot´s quasistatic equations, is consistent with the measured frequency dependent dispersion of the apparent bulk modulus of the background matrix and the in-situ pore pressure response, which is caused by fluid pressure diffusion from the compliant fractures into the stiffer matrix. The observed fluid pressure diffusion is causally related to the numerically quantified intrinsic attenuation at seismic frequencies, which is a major contributor to the dissipation of seismic waves. Our analysis supports the use of a simple approximation of fractures as compliant and planar inclusions in numerical simulations based on linear poroelasticity.