In the context of digital rock analysis, pore-scale imaging of multiphase flow experiments using X-ray microtomography can be used to obtain fundamental insights into pore-scale displacement physics. This provides a basis to better calibrate numerical pore-scale simulators, or it can be used to understand local fluid distributions, while simultaneously measuring average properties, equivalent to a traditional SCAL experiment. Imaging studies in the literature have historically been conducted on small water-wet plugs, using kerosene, or another refined oil, as the non-wetting phase. Prior to conducting waterflood experiments, the initial water saturation has been established by dynamic flooding. The disadvantage with this is that a nonuniform saturation profile is established due to the capillary end effect. This will result in a higher average initial water saturation compared with, for instance, standard SCAL techniques, such as the porous-plate method or centrifugation.
In this paper, a methodology for initializing multiple small rock samples to the same connate water saturation and wettability state has been developed by adopting best SCAL practices, namely the porous-plate method or centrifugation using crude oil, followed by aging. We drill multiple small plugs from a full-size SCAL core sample, without losing capillary continuity with the base of the original sample. In the example presented, for Bentheimer sandstone, the initial saturation was established using centrifugation. The experiment is designed to prevent a nonuniform saturation profile in the small plugs. We use in-situ imaging to determine the water saturation after primary drainage and show that it is indeed uniform across the sample with a value consistent with larger-scale SCAL measurements and the measured mercury-injection capillary pressure. We also show that a significant wettability alteration had occurred by measuring in-situ contact angles.
