THE PERMEABILITY OF OIL-BEARING STRATA 381 



of the dependence of the coefficient of increase in resistance Q on the perme- 

 abihty K . This is done in the following way: 



(a) For all Avells in which cores of the given stratum were selected and the 

 permeability determined, the mean values of the permeabihty and the coef- 

 ficient of increase in resistance are determined. 



(b) Points, the coordinates of which correspond to the average value of 

 the permeabihty K and the coefficient of increase in resistance Q ob- 

 tained from each of the wells are plotted on logarithmic paper. 



(c) The axis which has the values of permeabihty, is split up into inter- 

 vals (for example, 10-20, 20-50 etc.) and for each interval the most probable 

 value of Q is found (that value, with respect to which a half of the points 

 in the given interval is above, and half below); this value is carried on to 

 the middle of the interval; 



(d) From the points obtained in this way and with some averaging (to 

 obtain a smooth curve) a curve is drawn for the dependence Q = /{K^^^. 



In order to obtain the curve Q = f{K) with sufficient accuracy, the 

 number of points on the graph should be sufficiently large (not less than 15). 



On both sides of the main curve Q = f{Kper) auxiliary curves are drawn 

 so that between them and the main curve there is a quarter of the total 

 number of points on the graph. The distance from the main curve to the 

 auxiliary curve in a direction parallel to the K axis gives the probable 

 error in the results of determining the permeability. 



3. To determine the permeability from the specific resistance the coeffi- 

 cient of increase in resistance, Q, is found, and then from the curve Q=/{K ) 

 for a given stratum, the corresponding value of permeability K is calcu- 

 lated. 



4. In principle the method for determining permeability from the specific 

 resistance is applicable only to those cases where the petroleum-bearing 

 stratum is at a distance from the vipper surface of the petroleum reservoir 

 and where this stratum has no bottom water or an intermediate zone (the 

 transition zone from the purely petroleum to the purely water part of the 

 stratum). 



The method of determining permeability from the specific resistance of 

 the strata containing an intermediate zone in the upper part is applicable 

 only to thick strata provided: 



(a) It is separated from the water-bearing part by a bed of clay; 



(b) It is at a considerable (for example, more than 10 m) distance along 

 the vertical from the upper surface of the water. 



Usually the error in the determination of permeability from the specific 

 resistance is 30-50% and greater. For some strata the error is so great that 



