Ch. 32] FACTORS AFFECTING RESERVOIR PROPERTIES 603 



pore volume 



m = — 



interstitial surface area 



or 



/ 



m = — 

 A 



This concept of capillary rise is in error for porous media, because 

 water moves into a porous structure without completely filling the 

 pores. Thus the measurement of the capillary rise, that is, the height 

 to which water will fill the pores, is uncertain. 



It should be mentioned that the Kozeny-Carman law as stated above 

 has been formulated for the flow of one fluid through a homogeneous 

 porous medium. When two fluids occupy the pore spaces in a sand 

 bed, the situation is much more complex. One way to treat the prob- 

 lem is to consider one fluid moving through a matrix having an in- 

 terstitial surface made up partly of rock and partly of the other 

 fluid. This is very difficult to treat, and only very limited approxima- 

 tions for the amounts of rock and fluid surfaces can be made. Some 

 attempt to study this problem was made by Rose and Bruce (1949), 

 but the treatment proposed by them is acknowledged to be only very 

 approximate. It is felt that the clue to a statistical description of 

 relative permeability phenomena lies in understanding the Kozeny- 

 Carman law and correlating it with the other physical laws governing 

 the flow of fluids through porous media. 



The above discussion has dealt with the relationship of interstitial 

 surface area to permeability and to porosity. Actually, by measuring 

 permeability and porosity of a porous medium of known texture, it is 

 often possible to make an approximate calculation of the interstitial 

 surface area. The several methods for measuring interstitial surface 

 area are discussed in detail by Brunauer (1943). Perhaps the most 

 commonly used is the Brunauer, Emmett, and Teller method, which in- 

 volves the adsorption of a monomolecular layer of gas on the inter- 

 stitial surface of the porous medium. If the number of molecules on 

 the surface and the area occupied by one molecule are known, it is pos- 

 sible to calculate the interstitial surface. 



SEDIMENTARY FACTORS AFFECTING RESERVOIR PROPERTIES 



Nearly all the theoretical and much of the experimental work on the 

 behavior of fluids in porous media has been based on the idealized con- 



