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A pore-scale experimental investigation of microscopic steady-state flow during co-injection from very low to high flow rates in the pore space of a sandstone is applied using 4D synchrotron X-ray micro-tomography to advance our understanding of flow regimes. We report the results of micro-CT imaging experiments directly visualizing the simultaneous flow of both a wetting and a non-wetting fluid through a Bentheimer sandstone, at pore-scale resolution. For small flow rates, both fluids flow through unchanging, distinct, bicontinuous 3D pathways. At higher flow rates, however, the non-wetting fluid continually breaks up into discrete ganglia; these are then advected through the medium. We propose that the non-wetting fluid breaks up when the sum of the viscous forces exerted by the wetting and the non-wetting fluids exceed the capillary forces at the pore scale.
We imaged the steady-state flow of brine and decane at different fractional flows during dual injection in a micro-porous limestone using X-ray micro-tomography. We applied differential imaging on Estaillades carbonate to (a) distinguish micro-porous regions from macro-pores, and (b) determine fluid phase pore occupancy and relative permeability at a capillary number, Ca = 7.3×10-6. The sample porosity was approximately 28 %, with 7% in macro-pores and 21% in pores that could not be directly resolved (micro-porosity). We find that, in addition to brine and decane, a fraction of the macroscopic pore space contains an intermittent phase, which is occupied either by brine or oil during the hour-long scan time. Furthermore, fluid occupancy in micro-porosity was classified into three sub-phases: micro-pore space with oil, micro-pore space with brine, and micro pores partially filled with oil and brine.