Four-dimensional X-ray micro-tomography imaging of dynamic processes in geosciences

Abstract

The dynamic response of rocks to thermal, hydrodynamical, mechanical, and geochemical solicitations is of fundamental interest in several disciplines of geosciences, including geo-engineering, geophysics, rock physics, hydrology, mineralogy, and environmental and soil sciences. From crystal shape to rock microstructure or pore space and fluid distribution, parameters characterizing the rock physico-chemical properties evolve at different time and spatial scales. X-ray micro-tomography (XMT), as a non-invasive and non-destructive imaging technique, offers an unprecedented opportunity to add the fourth dimension, i.e. time, to the three-dimensional spatial visualization of rock and mineral microstructures. The technique is increasingly used to explore dynamic processes in porous and fractured rocks, thanks to synchrotron sources and laboratory XMT scanners, new generations of detectors, and increasing computational power. Image processing allows for tracking the evolution of the fluid–fluid or fluid–mineral interfaces as well as measuring incremental deformations, as rocks deform and react through time under in situ conditions of the sub-surface. Here, we review recent advances in 4D X-ray micro-tomography applied to thermo-hydro-mechano-chemical (THMC) sub-surface processes where fluids, porosity, minerals, and rock microstructures evolve together.