An Experimental Study of the Effect of Gravity on Foam in Fractures

In this study, to investigate how gravity affects foam in fractures, we carry out seven sets of foam-scan experiments on three glass model fractures (model A, model B and model C) with a hydraulic aperture of 78, 98 and 128 microns respectively. We compare the behaviour of foam in the models placed horizontally and vertically. We find that stable foam is created and reaches local equilibrium in all horizontal-flow experiments in 3 models. Foam gets weaker as the hydraulic aperture of fracture becomes larger. In sideways flow experiments, the effect of gravity on foam stability is less in model A. As the hydraulic aperture increases, the effect of gravity is more pronounced. Due to gravity, drier and coarser foam propagates at the top of the fractures, wetter and finer foam along the bottom. Foam is stable during the sideways flow experiments in model A and B, at all foam qualities. In model C, foam breakage alternates with re-generation near the top at foam qualities larger than 0.94. It is concluded that the application of foam in vertical natural fractures (meters tall and tens of meter long) with an aperture up to hundreds of microns is problematic.