Permeabilities of Water-Oil Two-Phase Flow in Capillary Fractures with Different Wettabilities

The influence of wettability on the permeability performance of water-oil two-phase flow has attracted increasing attention. Dispersed flow and stratified flow are two flow regimes for water-oil two-phase flow in capillary fractures. The theoretical models of relative permeability considering wettability were developed for these two water-oil flow regimes from the momentum equations of the two-fluid model. Wettability coefficients were proposed to study the impact of wettability on relative permeabilities. Experiments were conducted to study the relative permeabilities of laminar water-oil two-phase flow in water-saturated and oil-saturated horizontal capillary fractures with different hydraulic diameters. These fractures were made of polymethylmethacrylate (PMMA) and polytetrafluoroethylene (PTFE), which had different surface wettabilities. In this experiment, the regimes are dispersed flow and stratified flow. The results show that the effect of wettability on the relative permeabilities increases as the hydraulic diameters of capillary fractures decrease for water-oil two-phase flow. The relative permeabilities in a water-saturated capillary fracture are higher than those in an oil-saturated capillary fracture of the same material. The relative permeabilities in a PTFE capillary fracture are larger than those in a PMMA capillary fracture under the same saturated condition. Wettability has little effect on the permeability performances of water-oil two-phase flow in water-saturated capillary fractures, but is significant for those in oil-saturated capillary fractures.