Abstract

We report petrophysical changes on a suite of Berea sandstones undergoing heat-cycling treatment. Crack concentrations from experimental data (e.g., nuclear magnetic resonance [NMR], mercury injection, and thin sections) are compared with results from a modified Cheng-Toksöz velocity inversion model using a differential effective medium to investigate the physical significance of the inversion. We propose a deterministic methodology to estimate grain properties, pore-crack aspect-ratio spectrum, and consistent pore-crack insertion ordering for the inversion. Our inversion scheme reproduces velocity profiles to within ±5%. Moreover, we demonstrate for the first time that velocity inversion can resolve the increase in concentrations of small cracks as rock samples are heat-treated. The crack concentration changes calculated from the inversion are consistent with other independent experimental data of porosity, density, thin-section observations, NMR spectra, and mercury injection spectra, lending credence to the use of velocity inversion in microstructural characterization.

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