An experimental investigation of retention of liquids in corners of a square capillary

Abstract

The retention of liquids in the corners of a 0.03-cm square capillary after the passage of a gas slug was studied experimentally as a function of capillary number in the range from 10 −3 to 10 −6. In gas–wetting liquid systems, for capillary number greater than 5×10 −4, the retention of a wetting liquid in the corners showed a strong dependence on the capillary number; i.e., the retention of the liquid decreased with decreasing capillary number. For capillary number less than 10 −4, the retention of a wetting liquid was found to be determined by the capillary forces and the rate (or viscous) effect was negligible. In gas–oil–water systems involving double displacements—gas was displacing oil which was in turn displacing water—the total retention of water and oil vs capillary number curve showed the same trend as the retention of a wetting phase in a gas–wetting liquid system. However, because of the viscous effect, the water retention showed a continuous decrease with decreasing capillary number and could be lower than the capillary equilibrium value at very low capillary numbers. As a result of this, the oil retention vs capillary number curve in the double displacement process showed a minimum; i.e., oil retention increased with decreasing capillary number in the range of very low capillary numbers.