X-ray imaging of water motion during capillary imbibition: Geometry and kinetics of water front in intact and damaged porous rocks

Abstract

[1] Imaging fluid flow in porous rocks is a constant challenge in Earth sciences. We present the results of an experimental study to image capillary imbibition processes using an industrial X-ray scanner to investigate fluid motion processes in relation with microstructural properties for various porous rocks. Two-dimensional density maps obtained at a constant time step of about 3 s in standard capillary rise experiments on intact and damaged rock samples are analyzed. Both sandstones and carbonate rocks have been studied. The geometry of the water front depends on the sample geometry but also on the rock microstructure and the dynamics of capillary processes as its curvature changes during water rising. We discuss the effect of anisotropy, heterogeneity, microstructures, and driving forces on the kinetics and geometry of the water front. Once a good knowledge of the intact rock behavior was achieved, mechanical damage was induced in creep experiments at increasing stress levels with a continuous recording of acoustic emissions. The density maps obtained during imbibition under the scanner were analyzed to show how the mechanical deformation alters the fluid displacement patterns. We found that the velocity and the geometry of the waterfront are strongly disturbed in comparison to the intact rock. However, our study was not really conclusive on the effect of fractures on fluid flow patterns. Conducting capillary imbibition experiments coupled with imaging techniques using an X-ray scanner is a powerful technique to image fluid flow patterns in reservoir rocks and how they are affected by deformation.