DYNAMICS OF 2-PHASE FLUID INTERFACES IN RANDOM POROUS-MEDIA

Explicit account is given of the nonlocal dynamics tin a quasistatic a pproximation) involved in two-phase fluid dynamics quantifying flow th rough porous media. The results are used to derive the dynamical equat ion of motion of a Darcy-scale interfacial fluid front. We consider th e cases of invasion and imbibition separately, and point out the featu res responsible for the different depinning exponents observed in the two cases. A Flory-type scaling analysis is also performed on this mod el, yielding a roughness exponent alpha = 3/4 in a range of intermedia te length scales-in good agreement with experimental observations. Pos sible reasons are outlined for the different universality classes of e xponents observed during imbibition experiments.