Chap. 11] 



GEOPHYSICAL WELL TESTING 



837 



section of the Maeotic below is again indicated by the irregular saw- 

 toothed appearance of porosity and resistivity curves. In this section, 

 correlations have been made over distances of the order of 50 miles. 

 In some areas in this country, long-distance correlations are likewise 

 possible.^" Ver}^ good correlations are the rule in the mid-continent 

 fields.""' 



Fig. 11-13 is an outstanding example of how electrical logging may be 

 applied to indicate productive horizons. In this section of the Maracaibo 

 field, the three important oil horizons are very well indicated, as are the 

 depths to correct water shutoff and the low-resistivity clay formations. 

 In some fields a direct proportionality has been established between re- 

 sistivity and productivity of oil horizons. At Grozny, for instance (Fig. 

 11-14), a high resistivity of the H horizon corresponds to gusher produc- 



FiG. 11-12. Resistivity and porosity correlation of eight wells in the Gorgoteni 

 field, Rumania (after Schlumberger). 



tion and an intermediate resistivity (well 2), to oil shows with water. In 

 well 3, where the amplitude is about the same as that of other beds, the 

 horizon is dry. 



Electrical logging has become dail}' routine in many oil-producing fields 

 and wildcat wells. Results are accumulated at a much more extensive 

 rate than the few examples given above indicate. 



II. TEMPERATURE MEASUREMENTS 



It is an age-old belief that the interior of the earth is hot, and it is a 

 matter of long-standing experience that ground temperature increases with 



i« A.A.P.G. Bull. No. 23 (11), 1622-1626 (Nov., 1939). 

 loa Personal communication from H. Guyod. 



