Influence of physical parameters on the “viscous fingers” structure

Abstract

Displacement of oil by less viscous media leads to instability of the front and the formation of “viscous fingers”, the structure of which depends on various physical parameters. The most informative dynamics of the change in the interface between the injected fluid and the displaced medium with a change in physical parameters can be studied using the Hele-Show cell. The use of a cell with a small gap makes it possible to track the effect of changes in surface tension (at the interface, oil displacing liquid) on the formation of “viscous fingers”. The results of an experimental study of the development of “viscous fingers” during unstable displacement of oil by water and an aqueous solution of surfactants from the Hele-Show cell are presented. Physical parameters were changed: temperature, dynamic viscosity, surface tension and flow regimes influencing the formation of “viscous fingers”. It was found that an increase in the displacement fluid flow rate leads to an increase in the area of coverage and a decrease in the width of the “viscous fingers”. After the breakthrough, a drop in the share of oil displacement is observed. The use of surfactants reduces the surface tension at the interface between the two media, increases the coverage and significantly reduces the number and size of residual oil pillars, which leads to an increase in displacement efficiency. An increase in temperature decreases the viscosity ratio of the displaced and displaced fluid, which leads to less intensive tongue development and more efficient oil displacement. Fractal analysis of the dimensions of «viscous fingers» made it possible to establish a correlation between fractal dimension and displacement efficiency, an increase in fractal dimension corresponds to an increase in oil recovery. Thus, the change in physical parameters during unstable displacement makes it possible to find the determining factors for increasing oil recovery at various stages of displacement.