Real-time visualization and investigation of dynamic gas snap-off mechanisms in 2-D micro channels

Abstract

Capillary snap-off of gas phase usually occurs during a water invasion process and it causes the entrapment of gas phase in a gas-water multiphase flow scenario. In this paper, the real-time visualization and investigation of dynamic gas snap-off mechanisms under three levels of capillary flow regime were achieved in a 2-D micro channel with special designed continuously varying pore throat sizes. The gas-water flow patterns revealed that water film evolution existed in two distinct directions in the channel: one as the wetting film spreading along the surface wall of the channel, and the other as the wetting film swelling in the longitudinal direction of the channel. Further analysis indicated that a competition was involved among these two evolving directions depending on the water injection rate and it was found that the wetting film spreading became preponderant with the declining water injection rate. Meanwhile, dimensionless capillary pressure calculation by Roof’s theory was experimentally employed for the first time on noncircular cross sectional capillary channel to predict the gas bubble evolution criterion before snap-off. The experimental results have shown a satisfactory match with the theoretical calculation thus proved the feasibility of applying Roof’s theory on gas snap-off judgment in 2-D micromodels. These findings will facilitate a better understanding of multiphase flow behaviors and capillary induced gas phase snap-off in a porous media with varying pore throats.