Micro Particle Image Velocimetry (micro-PIV) to Quantify Multiphase Flow In Micromodels

Abstract:

The physical mechanisms of multiphase flow in porous media are more complex in comparison to single-phase flow. Although experimental and numerical results at all scales are useful to develop understanding, fluid flow ultimately occurs through the pore and fracture networks of rocks, sands, and shales. Accordingly, this talk focuses on pore-scale displacement mechanisms obtained using etched-silicon micromodels. Such micromodels have the pore network pattern and pore sizes of a real rock etched into a silicon wafer. Importantly, these micromodels permit direct, high-magnification, time-lapse observations of fluid movement through pores.

A significant new tool in microfluidic research is particle image velocity (micro-PIV) to monitor pore-scale velocity distributions and their history. We make such measurements in micromodels using simple optical equipment combined with efficient image acquisition and processing. Pore-scale velocity distributions are obtained for single-phase flow in porous media with typical pore sizes of 5 to 40 µm at vector-grid resolutions as fine as 2 µm by 2 µm. The single-phase images and measurements are in excellent agreement with numerical simulations. Micro-PIV during unstable immiscible two-phase flow experiments (drainage of the wetting phase) reveals that flow is oscillatory long before the arrival of the invading interface. The dynamics include abrupt changes of velocity magnitude and direction as well as interfacial jumps. Following the passage of the front, dissipative events, such as eddies and recirculations within the aqueous phase are observed when interrogated with micro-PIV. These observations of complex interface dynamics at the pore scale motivate reconsideration of the standard multiphase extension of Darcy’s law that commonly neglects interfacial and viscous dissipation.