THE PERMEABILITY OF OIL-BEARING STRATA 353 



The relative deviation of the accepted value q^ from the actual reaches 

 a value of the order of 0.1-0.3, especially in the case when the average 

 value is taken for the specific resistance of the water-bearing stratum. 



The connection between the coefficient of increase in resistance and the 

 coefficient of water saturation K^^ is approximately expressed by the 

 formulae (3,10) 



Q = -^ or Kr.u. = Q-1I-, (4) 



where ;i is a certain power close to two. 



If dQ is the error in determining the coefficient of increase in resistance, 

 and dn the deviation of the value for the power from its actual value, the 

 error in determining the coefficient of residual water saturation will be* 



--n -i -^ -1 



dKr.u, = ^-%^dQ+%—dn = -Q " dQ+-\Q "inQdn. 



9Q dn n 



n 



In accordance with this the relative error in the coefficient of residual 

 water saturation will be 



dKr.u, IdQ I 



—f? — = -pr-\ ^ in (2dn. 



Kr.w n {J w^ 



If we assume that n = 2, the deviation of the actual value from that taken 



dn = 0.1, the coefficient of increase in resistance Q = 100 and the relative 



. . , . . dQ 



error m its determination — = 0.3, then we obtain 



Q 



dKr.u, 0.3 , 0.1 In 100 ^^, 



As can be seen, despite the considerable errors in the original data, the 

 coefficient of the residual water saturation (providing there are no large 

 errors) is determined comparatively accurately}". 



To determine the closer connection of the coefficient of the residual 

 water saturation with the permeabihty of the strata let us compare the results 

 in determining permeability with the data of permeability established from 

 measurements on samples. 



* We will only take the value of error without considering its sign. 



t If re differs considerably from 2, then the error in determining Kj. ^ is greater. 



Applied geophysics 23 



