Alteration of seismic wave properties and fluid permeability in sandstonesdue to microfracturing

Rock microfracturing significantly affects elastic and anelastic parameters as well as transport properties. Several rock models are proposed in liter ature relating rock microfractures and cracks to the effective velocities. However, the mechanisms involved in the attenuation of seismic waves still need further investigation in order to properly relate attenuation to fract uring. Laboratory measurements of ultrasonic wave propagation are performed on dry sandstones during increasing fracturing of the samples. Perpendicul ar to the loading axis the wave velocities decrease and attenuation increas e. The observed decrease of wave velocity is a measure for the crack densit y of the newly formed cracks. Utilising crack densities and microstructural parameters the attenuation behaviour is interpreted in terms of the mechan isms friction and scattering. On the same rock samples the effect of fractu ring on water transport is investigated. Measurements before and after the mechanical fracturing show a decrease of permeability in loading direction. The changes in seismic parameters and permeability are interpreted by diff erent variations in rock microstructure. This should be considered when rel ating seismic and transport rock properties. (C) 2000 Elsevier Science Ltd. All rights reserved.