Digital rock physics: numerical prediction of pressure-dependent ultrasonic velocities using micro-CT imaging

Digital rock physics combines modern microscopic imaging with advanced numerical simulations to analyse the physical properties of rocks. Elastic-wave propagation modelling based on the microstructure images is used to estimate the effective elastic properties of the rock. The goal of this paper is to describe and understand how laboratory experiments compare with digital rock physics results using Berea sandstone. We experimentally measure pressure-dependent ultrasonic velocities and the pore size distribution. The effective elastic properties resulting from numerical simulations are based on microcomputed tomography (micro-CT) images, which are systematically stiffer than the laboratory measures. Because the tomographic images do not resolve the small-scale pore and crack network of the sample, we hypothesize that the numerical overprediction is attributable to the smallest pores and grain-to-grain contacts that are missing in the images. To reconcile the difference between numerical and experimental data, we suggest to use a grain boundary reconstruction algorithm. This allows to implement and approximate so far unresolved features in the virtual rock model. As a result, we can predict pressure-dependent effective velocity using micro-CT images.