592 kussell-dickey. POROSITY AND PERMEABILITY [Ch. 32 



more than for the same oil saturations in two-phase flow. The isoperms 

 for all components are independent of the viscosity of the oil phase. 

 Points determined by kerosene and points that use a more viscous 

 blended oil fall along the same isoperms. And, finally, these authors 

 conclude that the presence of appreciable amounts of all three phases 

 in a flowing stream in equilibrium with the fluid in the pore space is 

 limited to a relatively small region of pore composition. 



More recently, Morse, Terwilliger, and Yuster (1947) made experi- 

 mental measurements of relative permeability in two fluid-phase sys- 

 tems. In this method a section of core is placed at each end of and 

 in capillary contact with the sample to be measured. Mixing of the 

 two fluids occurs in the first section, and the end effect of the wetting 

 phase piling up presumably occurs in the third section. It is probable 

 that simultaneous parallel flow of the two fluids takes place in the 

 center section (or sample). This experimental technique appears to 

 be convenient for some routine work. However, with this procedure 

 it is not possible to measure the pressure gradient separately in each 

 of the flowing phases, or to maintain a pressure difference between 

 phases (capillary pressure). It is also necessary to operate this equip- 

 ment at flow rates which are very large compared to those encountered 

 in an actual petroleum reservoir. At these rates, it is probable that 

 some sort of slug flow may be encountered, that is, alternate slugs of 

 each of the fluids. Rose (1948) and Rose and Bruce (1949) indicate a 

 possible method for computing relative permeabilities theoretically 

 from data taken from measurements of the capillary properties of 

 porous media. 



Capillary Properties 



The capillary properties (Rose and Bruce, 1949) of a porous medium 

 are determined by: (a) the geometrical configuration of the interstitial 

 spaces in the matrix, as discussed later in this chapter; (b) the 

 physical and chemical nature of the interstitial surfaces; (c) the physi- 

 cal and chemical properties of the fluid phases in contact with the in- 

 terstitial surfaces. The measurable macroscopic properties of a fine- 

 grained porous medium are porosity, permeability, and the capillary 

 pressure-saturation behavior of immiscible fluids in the medium. These 

 macroscopic properties depend on the microscopic properties classified 

 above. 



It has been recognized for some time that when two fluids occupy the 

 pore space in a porous medium the interfacial boundary between the 

 two fluids is curved (Leverett, 1941; Bruce and Welge, 1947). The 

 degree of this curvature is dependent on the size of the rock pores and 



