is absolute. It is measured parallel to the bedding plane by using dry air 

 through a clean, dry-rock specimen. 



Permeability Formulas 



The standard permeability formula is: 



uQL 



K = 



A (P, - P % ) 



K = Permeability, darcies 



u = Viscosity of fluid (cp) 



L — Length of plug (cm) 



A = Area of plug (cm 2 ) 



Pi= Upstream pressure (atm) 



Pg = Downstream pressure (atm) 



Q = Flow in center of core at mean pressure, 



ml /sec. 

 Q' = Flow at downstream face of core at pressure 



P 2 , ml/sec. 



When Q is measured with an incompressible liquid, Q and Q' are numer- 

 ically equal, and the formula becomes 



k c j\ r n> L i r- L ° 00 



K [in ma) — Lu{J -j where L — • 



Pi ■ P 2 



C can be made into a series of constants by setting P 2 at selected gauge pressures 

 and using the average barometric pressure as P g . 



Gas is compressible, and the Q in the fundamental formula refers to the 

 flow in the center of the core at mean pressure. This flow cannot be measured 

 directly, but the flow Q' at the downstream end of the core is measured and 

 translated to Q by means of Boyle's law. Thus, the standard permeability 

 formula when a gas is used as the measuring medium becomes 



K (in ma) — Lu(J -. where L — 



A ""~'" " (Pt+Pz) (Pt-P,) 



Again C can be made into a series of constants to facilitate calculations. 



The radial permeability formula introduces r ± and r 2 , the radius of the 

 core and the radius of the central hole respectively, in centimeters; when a gas 

 is used as the measuring medium, the formula becomes 



*l og Tl 



K < in md > = {Pl + Z P Ip, - p.) x TT 1 x Q ' 



'Log to base 10. 



239 



