An analysis has been made of relative permeability in simple capillary systems and it was found that the relative permeability to oil is not a single valued function of the saturation but is also dependent upon the viscosity ratio. It was also indicated that the relative permeability to the oil phase may be greater than one.
On fait une analyse de la perméabilité relative dans des systèmes capillaires simples, d'où il ressort que la perméabilité relative pour l'huile n'est pas une fonction de la seule saturation, mais dépend aussi du rapport des viscosités. I1 est montré également que la perméabilité relative pour la phase huile peut être supérieure à l'unité.
The relative permeability of a porous medium to a given phase in multiphase flow is usually considered to be dependent only upon the saturation and generally independent of the properties of the fluids involved. This concept is apparently supported by considerable experimental evidence as, for example, the work of Leverett (I) ** on high permeability (3.2 to 6.8 darcies) unconsolidated sands in which the viscosity was varied over a wide range (po/pw= 90.0 to 0.057) with practically no effect on the relative permeability saturation relationship. Recently, evidence has been accumulating from work performed by several laboratories (Petroleum Technologists, Inc., the Union Oil Company of California and others) which would cast some doubt on the validity of the foregoing generalization. It has been * Department of Engineering, University of California, ** Reference given at end of paper, Los Angeles, Ca. found that in some cases the relative permeability to oil with both water and oil in the core has been greater than one if the single phase permeability used in the calculations is that of water. While this may be somewhat disconcerting at first glance, further consideration of the phenomenon indicates that the results may be valid and not due to experimental errors.
One explanation which has been advanced to explain the behavior has been that it is due to the variable extent of hydration of the clay minerals present in the sand controlled by the saturation. The greater the water saturation, the greater will be the area of contact between water and clay minerals, and therefore, the greater the extent of swelling, with a corresponding reduction in permeability. While this would be possible if dual wettability were possible, it is difficult to conceive such restricted hydration of clays with the aqueous phase only at a distance of the order of the capillary size from some unhydrated clay. Another explanation is the migration of clay particles which were dislodged as a result of hydration which would give a lower standard for calculating relative permeability. However, this would not be a reversible phenomenon an