Immiscible displacement of viscosity-matched fluids in two-dimensional porous media

The effect of stabilization has been investigated experimentally when a nonwetting fluid is displacing a wetting fluid with the same viscosity in a two-dimensional porous medium. Experiments were done at different injection rates, with capillary numbers ranging from 10(-7) to 10(-4). The features of the front between the liquids were analyzed and found similar to those observed from invasion percolation models including a spatial gradient in the average pore threshold value, and gravitationally stabilized experiments. Front and structure of the trapped clusters of the invaded fluid at different capillary numbers are self-similar with the fractal dimensions D-b = 1.33 and D-b(m)=1.85, respectively. The dependence of the front width w(s) on the capillary C-a was found to be consistent with a power law w(s) similar to C-a(-alpha), with alpha=0.6. The dynamic exponent beta(d) approximate to 0.8 describing front width evolution as a function of time was determined by collapsing the density-density correlation function data. An analytical argument is presented to support the stabilization of the front owing to the viscous effects.