352 S. G. KoMAROv and Z. I. Keivsar 



direct connection between the coefficient of increase in resistance Q and the 

 permeabihty K p^^- 



To determine the permeabihty of the petroleum-bearing Devonian sand- 

 stone the appropriate value of permeability K , after having determined 

 its coefficient of increase in resistance Q, should be determined from curve 3 

 (Fig. 1). 



The method of determining permeability from the specific resistance in 

 principle is applicable only in those cases where the studied petroleum- 

 bearing stratum is at a distance from the contour of petroleum-bearing 

 deposits. This is connected with the fact that close to the contour of the 

 petroleum-bearing deposits or the intermediate zone in the stratum the 

 water content will exceed the residual water saturation. 



In thick strata containing bottom water, the method is apphcable only 

 to the upper part of the stratum at a considerable (for example, greater 

 than 10 m) distance along the vertical from the surface of the water, or if 

 the petroleum-bearing part of the stratum is separated from the water- 

 bearing part by a layer of clay. 



AN ANALYSIS OF THE REASONS FOR ERRORS IN THE DETERMINATION OF 

 PERMEABILITY BY SPECIFIC RESISTANCE 



The error in the determination of the permeability of the petroleum- 

 bearing strata by the specific resistance is due to the eiTor in determining 

 the coefficient of the interstitial Avater saturation and the insufficiently close 

 connection between the coefficient of the interstitial water saturation and the 

 permeability of the stratum. The coefficient of the interstitial water satura- 

 tion is determined from the coefficient of increase in resistance Q. The 

 relative error dQjQ in determining the coefficient of increase in resistance 

 is equal to the sum of the relative error dgjQg, in determining the specific 

 resistance of the stratum and the relative deviation dq^JQ^, taken for 

 calculations of the value of the resistance of the water-bearing stratum 

 from its actual value. 



The error in determining the specific resistance from the results from the 

 data of lateral electrical logging is caused by the inaccuracy of the results 

 of the measurements of the apparent resistance, by the difference between 

 the actual probe curve and the calculated curve chosen for it and the insuffi- 

 ciently accurate consideration of the various factors (the well diameter, the 

 zone of penetration, heterogeneity of the stratum). On the whole, this error 

 is appreciable and can reach up to 30% {dg J q^ =0.3). 



