Experimental analysis of fluid displacement and viscous fingering instability in fractured porous medium: effect of injection rate

Viscous fingering instability has been studied empirically by miscible flow displacement. Despite numerous experimental studies, there is little information regarding the fractured porous medium. The tests have been conducted in a rectangular porous medium, and the fluid was driven in the longitudinal direction. The generated fingering patterns are demonstrated and discussed based on injection rate and fracture orientation. Three porous models with 0°, 45° and 90° fractures were used in order to study the effect of fracture orientation. Quantitative parameters of fingering instability, such as sweep efficiency, headway position, and breakthrough time, have been measured by image processing techniques using MATLAB. It is shown that by increasing the injection rate, the size of the finger patterns slightly increased. Moreover, the effects of fractures on displacement behaviors are shown and explained. According to the results, zero degree fracture altered the rate of sweep efficiency and tip position the more significantly than other fractures. Furthermore, it was observed that by changing the direction of fractures from parallel to perpendicular to the flow direction, the breakthrough time increased consequently.