Miscellaneous Subsurface Methods 



701 



millidarcys). If the permeability of this same rock should be 850 milli- 

 darcys, then 



/bo 560 



kr(y (65,20) = — = = 0.66 



k 850 



(15) 



which states that the relative permeability of the rock to oil at a fluid 

 saturation of 65 percent oil, 20 percent water, and 15 percent gas is 0.66 — 

 or that at this condition of saturation, the effective permeability of the 

 rock to oil is only about two-thirds or 66 percent of the permeability — so 

 great is the interference of the water and gas also occupying space in 

 the pores to the movement of the oil. 



Although only relatively few studies of the relationships between 



Wet Test Meter 



Hg. Manometer 



Air Supply 



Regulator 



- L, , . il Adjusting Head 



rn Core Holder Tf i i — 



Handle 



i. 



I^^ 



-Cam 



Figure 377. Permeameter used at University of Texas. Fancher-type core holder. 



effective or relative permeability and saturation have been published, the 

 data which are in the literature have some common characteristics. 

 Whether a fluid wets the minerals composing a rock is important in all 

 permeability-saturation relationships because that fluid phase which wets 

 the rock will separate the nonwetting phase from the walls of any pore 

 passageway; and, consequently, wettability determines the spacial distribu- 

 tion of fluids in a porous rock (fig. 376). Furthermore, wettability is a 

 relative term — immiscible fluids differ not only in wettability but also in 

 the fact that the fluid with greater wettability can displace the one of lesser 

 wettability if the opportunity to do so comes about. The amount and 

 distribution of each fluid phase determines the relative and effective perme- 



