Micro-models are microfluidic devices used to study the transport of fluids in porous media domains. Porous media relevant to subsurface engineering and reservoir applications are 3D in nature. In order to observe and measure the transport and behavior of nano-particles through such media, it is necessary to preserve the 3D characteristics of the relevant geometry and flow while facilitating observation. These requirements are met through the design of 2.5D micro-models which incorporate micro-channel networks with 3D wall structure albeit with one flat wall for observation. Our group has designed such 2.5D micro-models matching fourteen morphological and flow parameters to those of fully 3D actual reservoir rock samples (Boise sand-stone) at a resolutions of 10 microns (depth) and 25 microns (on the plane). This paper presents a novel method of measuring the geometry, 3D particle velocity, particle concentration and particle deposition measurements for flows in such 2.5D micro-models.
A Confocal Micro-Particle Image Velocimetry (CµPIV) technique along with associated post-processing algorithms is presented for obtaining three dimensional distributions of nano-particle velocity, concentrations at selected locations of the micro-model. Instantaneous particle deposition on the inner surfaces at selected regions of the micromodel is also presented. In addition, an in-situ, non-destructive method for measuring the geometry of the micro-model, including its depth, is described and demonstrated. The flow experiments used 860 nm fluorescence labeled polystyrene particles and the data were acquired using confocal laser scanning microscopy. Regular fluorescence microscopy was used for the in-situ geometry measurement along with the use of Rhodamine dye and a depth-to-fluorescence-intensity calibration, which is linear. Monochromatic excitation at a wavelength of 544 nm (green) produced by a HeNe continuous wave laser was used to excite the fluorescence-labeled nano-particles emitting at 612 nm (red). Confocal images were captured by a highly sensitive fluorescence detector photomultiplier tube. Results of detailed three dimensional velocity, particle concentration and instantaneous particle deposition from experiments conducted at flow rates of 100 nL/min are presented and discussed.
The three dimensional geometry reconstructed from fluorescence data was used as the computational domain to conduct numerical simulations of the flow in the as-tested micro-model for comparisons to experimental results. The flow simulation results is used to qualitatively compare with velocity distributions of the flowing particles. The comparison is qualitative because the particle sizes used in these experiments may not accurately follow the flow itself given the geometry of the micro-models. These larger particles were used for proof of concept purposes, but the techniques and algorithms used in this work will permit future use of particles as small as 50 nm.
|Acceptance of Terms and Conditions||Click here to agree|