Pore-scale Experimental Investigations of Immiscible Displacements in Capillary Tubes and Porous Micromodels

摘要

Owing to the complicated nature of a porous medium, study of dynamics of fluid flow in such structures is not straightforward. Therefore, researchers have been using simplified one-dimensional (1D) and two-dimensional (2D) porous media models like capillary tubes, micro-models and micro-fluidic devices to perform such studies. We utilized both of these categories to investigate different parameters affecting the flow of fluids in a porous medium. In 1D, capillary tubes of different cross-sectional shapes and several wetting fluids are used to investigate the evolution of dynamic contact angle with the meniscus velocity. The meniscus rise vs. time curves produced by Washburn's equation are improved by implementing our experimentally measured dynamic contact angle values into the Washburn's original equation. A general empirical correlation is presented for variation of normalized rise with dynamic contact angle as well. In the second category, a novel two-phase, two-field-of-view micro-Particle-Image-Velocimetry system is developed. It allows simultaneous study of flow fields at the pore- and micromodel-scales and provides a deeper insight into the distribution of fluids. The effect of change of flow rate on shear stress at the interface of invading and defending fluids in a designed pore-doublet configuration made of Polydimethylsiloxane (PDMS) is studied. The impact of local perturbations of velocity fields on displacement of non-wetting phase and the residual trapping is also discussed. We show that these effects produce extensively different distributions of the trapped non-wetting phase globules. A modified 2D X-ray micro-computed tomography image of Bentheimer sandstone is replicated on PDMS. Single-phase velocity measurements in these models afford valuable insights into the complicated flow patterns through a porous medium; whereas in two-phase flow tests, in addition to resolving the velocity fields in both fluids, effects of changes in invading wetting phase flow rate and viscosity on pore fluid configuration and residual trapping is investigated as well. Not only these results provide a valuable understanding of the complexities of flow through porous systems, but also they can be used to validate the numerical models of fluid flow through porous systems.