2-PHASE FLOW VISUALIZATION AND RELATIVE PERMEABILITY MEASUREMENT IN NATURAL ROUGH-WALLED ROCK FRACTURES

A laboratory flow apparatus was used to visualize and measure two-phas e gas-liquid flows in natural rough-walled rock fractures. Experiments at carefully controlled flow rate and pressure conditions have been p erformed using a natural fracture and three transparent fracture repli cas. Two-phase flow exhibited persistent instabilities with cyclic pre ssure and flow rate variations even under conditions of constant appli ed boundary conditions. Visual observations of changes in pore occupan cy showed that the instabilities could be explained as resulting from an interplay between capillary effects and pressure drop due to viscou s flow. Measurements of relative permeabilities indicated strong phase interference, with relative permeabilities reduced to very small valu es at intermediate saturations for both wetting and nonwetting phases. These results run counter to a conventional view of fracture relative permeabilities that assumes that the relative permeability of each ph ase is equal to its saturation, but the results are consistent with re cent models that view fractures as two-dimensional heterogeneous porou s media.