INFLUENCE OF CONTACT-ANGLE ON QUASI-STATIC FLUID INVASION OF POROUS-MEDIA

We present results of detailed simulations of capillary displacement in model two-dimensional porous media as a function of the contact angle of the invading fluid. In the nonwetting limit (=180°), growth patterns are fractal as in the invasion percolation model. As decreases, cooperative smoothing mechanisms involving neighboring throats become important. The typical width of invading fingers appears to diverge at a critical angle c, which depends on porosity. Above c the invaded pattern remains fractal at large scales. Below c the fluid floods the system uniformly. Probabilities of local interface instabilities are analyzed to elucidate these findings. © 1990 The American Physical Society.