Scaling dispersion during miscible displacement in heterogeneous porous media
Abstract
Accurately predicting dispersion of miscible fluids in porous media is crucial in controlling groundwater pollution, recovering petroleum, and operating chromatographs and catalytic reactors. The goal of this work is to increase the knowledge of dispersion during miscible displacement in porous media by studying the effect of the system length scale and different permeability distributions on dispersion. Dispersion in both homogeneous and heterogeneous models of relative dimensions 1, 2 and 4 was investigated experimentally for flow out of the diffusion-dominated mixing regime. Several arrangements of three distinct permeabilities in the three different sized models were studied. It was found that: (1) the dispersion coefficient was not a function of the length scale of the system for both homogeneous and heterogeneous porous media, provided the distribution of the permeabilities was identical in the heterogeneous systems of different length scale, (2) the dispersion varied substantially with different arrangements of the same permeabilities, and (3) the dispersion in some arrangements with ratios of permeabilities as great as ten was similar to that for homogeneous media. A random-walk model was used to simulate data for both heterogeneous and homogeneous systems. The simulation reproduced experimentally obtained data reasonably well with the exception in flow regions in heterogeneous systems where the local velocity was less than 0.002 cm/s. In light of the finding that a different arrangement of the same permeabilities produced widely varying dispersion, a new phenomenological model was developed that has yet to be calibrated. The model has a dispersivity that is a function of the size of the system and the flow regime of the mixing. Also, the uncertainty of the predicted dispersion is incorporated into the model. It is outlined how the new model can be calibrated.
Degree
Ph.D.
Advisors
Greenkorn, Purdue University.
Subject Area
Hydrology
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