Particle velocimetry analysis of immiscible two-phase flow in micromodels

We perform micro-PIV measurements in micromodels using very simple optical equipment combined with efficient image acquisition and processing. The pore-scale velocity distributions are obtained for single-phase flow in porous media with a typical pore size of 5-40 µm at a resolution of 1.8μm×1.8μm vector grid. Because the application of micro-PIV in micromodels is not standard, extensive effort is invested into validation of the experimental technique. The micro-PIV measurements are in very good agreement with numerical simulations of single-phase flows, for which the modeling is well established once the detailed pore geometry is specified and therefore serves as a reference. The experimental setup is then used with confidence to investigate the dynamics of immiscible two-phase flow in micromodels that represent natural complex porous media (e.g., sandstone). For unstable immiscible two-phase flow experiments, micro-PIV measurements indicate that the flow is highly oscillatory long before the arrival of the invading interface. The dynamics are accompanied with abrupt changes of velocity magnitude and flow direction, and interfacial jumps. Following the passage of the front, dissipative events, such as eddies within the aqueous phase, are observed in the micro-PIV results. These observations of complex interface dynamics at the pore scale motivate further measurement of multiphase fluid movement at the sub-pore scale and requisite modeling.