New Flow Regimes of Viscous Fingering Instabilities with Two Wells inside a Hele-Shaw Cell

Viscous fingering instability in miscible displacements is of particular interest to a variety of subsurface displacement processes including enhanced oil recovery, CO2 sequestration, hydrogen storage, and water contaminate remediation in aquifer and soil system. It typically happens when a less viscous fluid is displacing a more viscous fluid in porous media. In this study, a horizontal Hele-Shaw cell with the size of 20 cm*20 cm*0.08 cm is used to examine the miscible fingering instabilities. Two wells are drilled as injector and producer, with a distance of 9.43 cm in the diagonal direction of the Hele-Shaw cell. We then use the less viscous water to displace high viscous glycerol which initially saturates the cell. Two groups of experiments were conducted by either fixing the pressure or rate at the production end. The injection rates were varied from 0.1 mL/min to 0.2 mL/min, 0.5 mL/min, 1.0 mL/min, 2.0 mL/min, and 5 mL/min. Based on the observations and quantitative analysis, we identified five different flow regimes: (1) stable diffusion-dominated regime, (2) convection-dominated regime with noticeable fingering instabilities growing with time, (3) a short slow expansion regime of fingering chamber, (4) a fast shrinkage regime where the large chamber quickly shrinks to a small one after breakthrough, and (5) uniform expansion regime in which the chamber continues to grow without fingering instabilities observed. The last three regimes are reported for the first time. The timing and length of each regime depend on the injection rate and whether a fixed pressure or rate is used at the production end. The quantitative analysis was also conducted for more interesting features of the fingering instabilities in this specific flow geometry. This research provides new insights for the development and mechanisms of miscible fingering instabilities in the life cycle displacement processes.