- https://doi.org/10.1029/2019WR026396
- 10.1029/2019WR026396
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Abstract — In this work, we use a multi-scale experimental and modelling approach to address fundamental, unanswered questions relating pore-scale fluid dynamics and their upscaled, continuum representation in subsurface multiphase flow. We utilise core flooding experiments with micro X-Ray CT imaging to analyse the role of representative elementary volumes (REVs), hysteresis and heterogeneity in multiphase flow in two distinct water-wetting Bentheimer sandstone samples. Experimental observations resolve the pore space at 6 µm across a field of view up to 12 x 12 x 65 mm with simultaneous measurements of differential pressure during fluid flow. The REV for both porosity and capillary pressure is approximately 2mm for both samples. In contrast, due to capillary pressure heterogeneities, the REV for saturation exceeds 8mm, the largest scale investigated. Predictions of fluid connectivity and hysteresis during imbibition using the Land trapping model are validated; fluid connectivity can be used to predict imbibition flow properties in homogenous media. However, fluid connectivity is also influenced by heterogeneities at scales larger than the REV. Both pore- and continuum-scale fluid connectivity must be accounted for in models of upscaled flow properties. The complex interplay of pore accessibility, availability and snap-off in heterogeneous media plays a crucial role in controlling connectivity and trapping at the continuum scale. We develop a hysteretic, 3D numerical model with REV scale heterogeneities, which is largely able to predict the impacts of these multi-modal heterogeneities in low capillary number multiphase flow. The experimental dataset herein provides an excellent benchmark for future development of continuum scale modelling frameworks.