Capturing 3D water layers and water-filled micropores in carbonate rock by high-resolution neutron tomography

Abstract

Knowledge of micrometer-scale wetting layers and microporosity in rocks is crucial for a deeper understanding of immiscible fluid displacement, and especially capillary trapping. It is an established fact that the amount of capillary trapping is a result from the competition between flow via wetting layers and piston-like displacement. Despite the large amount of experimental work published, there are many open questions about fluid displacement mechanisms in complex porous media, particularly the role of microporosity in the disconnection and entrapment of the nonwetting phase. Here, we applied the state-of-the-art neutron tomography technique (with the best spatial resolution available at neutron imaging facilities) to reveal the 3D distribution of water layers and water-filled micropores in a carbonate rock. Our results revealed wetting layers with a non-uniform thickness distribution completely covering the rock surface. During imbibition at a low capillary number, a marked increase in the amount of water-filled micropores with the concomitant swelling of wetting layers were observed. This approach can be used as a platform to explore a huge range of interfacial phenomena, such as enhanced oil recovery and CO2 storage.