(230a) Miscible, Unstable Viscous Fingering Patterns in a Radial Hele-Shaw Cell 

Viscous fingering experiments were performed by injection of a shear-thinning non-Newtonian fluid into a radial Hele-Shaw cell filled with a less viscous fluid. Shear-thinning is a term used in rheology to describe a fluid that displays decreasing viscosity when subjected to shear (non-Newtonian properties). Many engineering applications related to enhanced recovery system, hydraulic fracturing and remediation take advantage of specific shear-thinning fluids in their process. The objective was to develop a method for testing fluids of differing dynamic viscosity to provide further insight into the size distribution of apertures carrying flow in aquifers. It is also of interest to understand unstable viscous displacement of a non-Newtonian fluid in radial injection/withdrawal configuration while investigating the dynamic interface subject to advective and diffusive processes (length of the finger, width of the channel and mixing zone).

The effect of flow rate, polymer concentration, and salt addition was also demonstrated. Dye tracer was mixed with the non-Newtonian fluid (Xanthan Gum (XG) T622, CP Kelco) before injection/withdrawal to capture images of resulting viscous fingering patterns when a less viscous fluid displaces a more viscous fluid (unstable case). The Hele-Shaw cell was constructed from two parallel smooth glass plates with an initial displacement of 5 mm. Shims were placed at the outer edge of the circular plate to create a variable aperture system for studying displacement and flow path selectivity. The effect of flow rate, polymer concentration, and salt addition was also demonstrated. Rheological characterization of guar gum (GG) and XG at various concentrations was also performed in order to constrain rheological behavior when it is used for future in-field measurements utilizing ground penetrating radar (GPR) to reveal aquifer system structure. These polymers were also characterized with the addition of salt, which is used as the conductive tracer for GPR, and low density glass bubbles for density adjustments. Rheological data for both GG and XG with and without salt additions will be presented, along with characterization and parameterization of unstable viscous fingering patterns. Guar gum was shown to have high error and poor experimental reproducibility while xanthan gum showed better reproducibility and optimal shear-thinning behavior.