Microscopic Particle Image Velocimetry Analysis of Multiphase Flow in a Porous Media Micromodel.

Pore-scale oil displacement behavior was investigated in a porous media micromodel using microscopic particle image velocimetry (μPIV). Porous media micromodels consisting of an ordered square array of cylindrical pillars with 50 and 70% porosities were fabricated with photolithography. The oil displacement was performed with the injection of water at flow rates of 37.5, 75, and 150 μL/h. These flow rates correspond to Reynolds number of 1.1 × 10, 2.2 × 10, and 4.4 × 10, respectively in the 50% porous channel, and 1.84 × 10, 3.69 × 10, and 7.38 × 10, respectively in the 70% porous channel. The capillary numbers for these flow rates are 2.18 × 10, 4.36 × 10, and 8.72 × 10, respectively in the 50% porous channel, and 1.56 × 10, 3.12 × 10, and 6.23 × 10, respectively in the 70% porous channel. The micromodel is initially saturated with oil, with the invading water phase following the path of least resistance as it displaces the oil. The μPIV data were used to construct probability density functions (PDFs) which show an initial, nonzero, peak in transverse velocity as the water enters the micromodel. The PDFs broaden with time, indicating that the water is spreading, before retracting to a peak velocity of 0 mm/s, indicating that the water displacement has achieved equilibrium. We developed a model based on conservation of mass to describe the efficiency of the displacement process. All flow conditions demonstrate peak displacement efficiency when the amount of oil phase displacement is ∼9 pore volumes in 50% porous channel and ∼4 pore volumes in 70% porous channel.