Ch. 32] 



PERMEABILITY 



589 



Leas has devised apparatus for measuring the permeability of porous 

 material to air with an accuracy sufficient for use in most petroleum- 

 reservoir engineering applications (in preparation). This permeameter 

 is shown schematically in Fig. 3. Mi is a manometer for measuring the 

 pressure drop in the air phase across the core; M 2 is a manometer for 

 measuring the absolute pressure within the system. The elements of 

 the pump for forcing air through the core are contained within the 

 dotted area of the diagram. Two bulbs are filled partially with water 



Flowmeter 



Fig. 3. The Carter gas permeameter. 



the rate of flow of which from B 2 to B x is controlled by valve V\. When 

 7i is opened slightly, water flows from B 2 to Bi at a steady rate. The 

 water entering B x decreases the air volume therein, and the air pressure 

 increases. Simultaneously the air pressure in B 2 decreases because of 

 the water flowing out. The net result is a pressure difference across 

 the core measured by the manometer M 1 . The flow is measured by 

 the displacement of a soap film up the bore of a vertical calibrated glass 

 tube. 



The permeability is calculated from Darcy's law: 



k = 



nqL 

 APA 



where k is the permeability in darcys, q the volume rate of flow in 

 cubic centimeters per second, fi the viscosity of gas in centipoises, L 

 the length of the core in centimeters, A the cross-sectional area of the 

 core in square centimeters, and AP the pressure difference across the 

 core in atmospheres. 



