Multiple scale structure of non wetting fluid invasion fronts in 3D model porous media

We report experimental measurements on the structure of invasion fronts obtained by slow vertical injection of liquid, non wetting, Wood metal into non consolidated crushed glass. The geometry of plane cuts of the invasion front both parallel and perpendicular to the flow direction is analysed. The structure of perpendicular cuts is self similar in a length scale range of 1 to 20 with a fractal dimension 1.65. Saturation profiles measured from parallel cuts are in qualitative agreement with invasion percolation models. Possible theoretical predictions for the geometry of horizontal cuts are discussed Mesures de la structure de fronts d'invasion obtenus par une injection verticale lente de metal de Wood non mouillant dans un massif de verre pile non consolide. On analyse la geometrie de coupes du front d'invasion perpendiculaires et paralleles a la direction d'ecoulement. Comparaison des profils des coupes paralleles avec les modeles de percolation