We present 3D images of wetting fluid (potassium iodide-doped water) spontaneously infiltrating into a dry Bentheimer sandstone core, a process called “imbibition”. High resolution (voxel size of 1.7 micron) X-ray tomograms were acquired under quasi-static conditions at four timepoints throughout the process, allowing for investigation of the evolution of water distribution and water-air interfaces within the porous sandstone architecture. The experiment was carried out in-situ: the sandstone sample was installed in the flow cell on the sample stage, hydraulic connections were attached to the fluid pump inside the X-ray cabinet, and fluid flow was carried out with the sample in place on the sample stage. This set-up resulted in almost-perfect registration of the successive 3D data sets, and also allowed for real-time dynamic 2D imaging of the fluid invasion via X-ray radiographic projections.
Imaging was carried out at the Australian National University (ANU) CTLab using a space-filling helical scanning trajectory [1] combined with a high-quality region-of-interest (ROI) scanning method. ROI scanning maximises resolution (while also preserving field of view- in this case 4.6 x 4.6 mm) by scanning an internal subsection of the sample, i.e. the flow cell and the very edge of the sample are not captured in the projections. In order to accomplish this, a quick, low-resolution 'reference scan' is acquired, followed by a full-resolution scan of the internal sub-region. The reference scan is reconstructed, and the (now known) features outside of the ROI are subtracted from the ROI projections [2]. Thus, the ROI data is able to be reconstructed, without artifacts, as if it were full-field data.
This data set comprises the highest-resolution tomographic images of in-situ multiphase flow processes within geologic materials acquired at the ANU CTLab to date.