X-ray nano-CT: A road towards 4D nanoscale data in Earth Science

X-ray nano-computed tomography (nano-CT) is an established method to obtain 3D spatial image information in static systems. This method has enabled researchers to access ever finer details of complex bulk structures in various fields. Within Eath Science, this is relevant for the study of nanoporous formations, such as chalk, revealing the pore network structures from which local petrophysical formation properties can be derived. Various dynamic processes are also occurring, or are dependent on features at, the nanoscale, like residual CO₂ trapping. Besides X-ray attenuation differences, phase contrast is another acquisition mode that allows for resolving different phases within the bulk. Imaging is limited by sample and feature size, time, as well as sample composition and stability. Today, high brilliance synchrotron X-ray sources allow for true nanometer resolution and acquisition times of minutes, rather than hours. Furthermore, recent advances in working at higher X-ray energies put imaging of X-ray sensitive aqueous systems within reach, without sample deterioration. We will illustrate the capacity of nano-CT on an example of static chalk data for deriving various formation properties. We will then give an overview of instrumental approaches for doing synchrotron nano-CT, experimental limitations, requirements, and illustrate how time resolved imaging (4D) of dynamic geological processes may be accomplished in the near future.