Three-phase Flow and Wettability Effects in Triangular Capillaries
We performed a series of two and three-phase flow experiments in capillary tubes with equilateral triangular cross-sections. We measured the flow rates of oil and water in water-wet tubes and compared them with predictions using an empirical theoretical expression for fluid conductance. Our results are consistent with a free boundary condition at the gas/liquid interface, and with a no-flow boundary at the oil/water interface, when water is stationary, and a condition between a no-flow and a free-boundary when oil and water flow simultaneously. By studying oils with different spreading coefficients we measured the circumstances when oil layers form, and we compared the results with a simple geometric argument for oil layer existence. We also studied flow in uniformly oil-wet tubes. Overall, the work verifies and calibrates theoretical expressions for fluid conductance and layer formation that can be inputted into pore level network models to predict macroscopic properties, such as relative permeability. We illustrated this approach by using our work to interpret three-phase relative permeability experiments on sandpacks.