X‐ray Microtomography of Intermittency in Multiphase Flow at Steady State Using a Differential Imaging Method. Issue 12 (8th December 2017)

• Record Type: Journal Article
• Authors: Gao, Ying; Lin, Qingyang; Bijeljic, Branko; Blunt, Martin J.
• Is Part Of: Water resources research. Volume 53:Issue 12(2017)
• Page Start: 10274
• Page End: 10292
• Publication Date: 2017-12-08
• Subjects: coinjection -- flow regimes -- differential imaging -- intermittency -- relative permeability; Hydrology -- Periodicals; 333.91
• DOI: 10.1002/2017WR021736
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: We imaged the steady state flow of brine and decane in Bentheimer sandstone. We devised an experimental method based on differential imaging to examine how flow rate impacts impact the pore‐scale distribution of fluids during coinjection. This allows us to elucidate flow regimes (connected, or breakup of the nonwetting phase pathways) for a range of fractional flows at two capillary numbers, Ca, namely 3.0 × 10 −7 and 7.5 × 10 −6 . At the lower Ca, for a fixed fractional flow, the two phases appear to flow in connected unchanging subnetworks of the pore space, consistent with conventional theory. At the higher Ca, we observed that a significant fraction of the pore space contained sometimes oil and sometimes brine during the 1 h scan: this intermittent occupancy, which was interpreted as regions of the pore space that contained both fluid phases for some time, is necessary to explain the flow and dynamic connectivity of the oil phase; pathways of always oil‐filled portions of the void space did not span the core. This phase was segmented from the differential image between the 30 wt % KI brine image and the scans taken at each fractional flow. Using the grey scale histogram distribution of the raw images, the oil proportion in the intermittent phase was calculated. The pressure drops at each fractional flow at low and high flow rates were measured by high‐precision differential pressure sensors. The relative permeabilities and fractional flow obtained by our experiment at the mm‐scale compare well with data from the literature on cm‐scale samples. Key Points: Differential imaging of fluid configurations during steady state brine/decane fractional flow coinjection at low and high capillary numbers At low Ca number the two phases flow in their own connected pathways as expected, while an intermittent phase was observed at high Ca number The relative permeability measured on our mm‐scale core shows a good agreement with conventional experiments on cm‐sized systems