4D Imaging of Two‐Phase Flow in Porous Media Using Laboratory‐Based Micro‐Computed Tomography.

Dynamic three‐dimensional computed tomography (CT) imaging of liquid transport in porous media has primarily been conducted at high brilliance synchrotrons thus allowing fast, sometimes sub‐second, temporal resolution to be obtained. University laboratory CT instruments lack the photon flux available at synchrotrons, limiting the obtainable spatiotemporal resolution. Here, we discuss our experiences with instrumentation and software methods to conduct time‐resolved micro‐computed tomography (4D‐CT) experiments of flow in porous media, based on a conventional CT instrument operated with a highly undersampled number of projections. An experimental stage outfitted with syringe pumps placed on a slip ring allowed two‐phase flow experiments to be carried out with continuous unidirectional rotation and without obstruction of the liquid supply lines. An iterative reconstruction algorithm based on a priori information was used to provide high image quality and ∼30 s time resolution despite the few and low‐exposed projections compared to standard protocols. The experimental technique was demonstrated with imbibition and drainage in glass bead‐pack and Bentheimer sandstone samples with sub‐minute temporal resolution, allowing the liquid configurations just before and after fast dynamic phenomena such as cooperative pore‐filling events and Haines jumps to be captured. Power law scaling exponents for burst volumes associated with imbibition and drainage were estimated and compared with the literature. That 4D‐CT experiments can be carried out using conventional CT instruments to challenge contemporary permeability models is of high importance for many geo‐, bio‐ and environmental physics challenges. Plain Language Summary: Computed Tomography or CT is well‐known as a technique for investigating objects in 3D non‐destructively. In principle, 3D movies, referred to as "dynamic CT" or "4D CT" is a simple extension, requiring just a series of standard CT experiments to be carried out in sequence. In practice, however, there is a high demand for clever methods and algorithms that can simultaneously obtain high spatial and temporal resolutions. When more than one fluid is being transported through a porous medium, a plethora of phenomena take place, and 4D‐CT has proven a powerful tool to better understand the physics of porous media. Most 4D‐CT studies in the past have been carried out at synchrotron facilities, which are extremely high flux X‐ray sources, but also a scarce and expensive resource. We describe our experiences with 4D‐CT measurements of fluid transport in porous media, as performed in our home laboratory. Key Points: Time‐resolved 3D imaging of flow in porous mediaDynamic micro‐computed tomography [ABSTRACT FROM AUTHOR]