M. Ferer et Dh. Smith, DYNAMICS OF GROWING INTERFACES FROM THE SIMULATION OF UNSTABLE FLOW IN RANDOM-MEDIA, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 49(5), 1994, pp. 4114-4120
Viscous fingering in random porous media is encountered in many applic
ations of two-phase flow, where the interface is unstable because the
ratio of the viscosity of the displaced fluid to that of the injected
fluid is large. In these applications, including enhanced oil recovery
, characterization of the width of the interface is an important conce
rn. In the limit of stable flow, the interfacial width had been found
to grow as w almost-equal-to t(beta), where beta almost-equal-to 0.66,
approximately independent of capillary number. To study the same beha
vior for the unstable case, we have simulated flow in two-dimensional
random porous media using a standard model with different viscosity ra
tios and zero capillary pressure. When the injected fluid has zero vis
cosity, viscosity ratio M = infinity, the interfacial width has the ex
pected self-similar diffusion-limited-aggregation-like behavior. For s
maller viscosity ratios, the flow is self-affine with beta = 0.66 +/-
0.04, which is the same value that had been observed in studies of sta
ble flow. Furthermore, the crossover from self-similar fractal flow to
self-affine fractal flow is observed to scale with the same ''charact
eristic'' time, tau = M0.17, that had been found to scale the average
interface position. This ''fractal'' scaling of the crossover leads to
definite predictions about the viscosity-ratio dependence of the ampl
itudes associated with interfacial position and interfacial width.