1092 



EXPLORATION GEOPHYSICS 



and other parameters have all been utilized as a means for obtaining supplementary 

 data for guidance of the drilling and completion operations, and for structural cor- 

 relation with other wells. 



An illustration of resistivity measurements on core samples is shown in Figure 

 682. For this work, resistivity measurements were made on the cores and plotted 



vm 





Fig. 682. — Comparison of A, geological log; B, resis- 

 tivity measurements on core specimens; C, resistivity 

 log in bore hole for a well in the San Joaquin Valley, 

 California. 



against depth (curve B) in conjunction with the geological log (A) determined by 

 inspection of the cores. Upon completion of the well an electrical log was run (curve 

 C). There is a good general agreement between the logs, although as would be ex- 

 pected, the core log (B) lacks the good detail shown by the electrical log (C) of 

 the hole. This lack of detail is due largely to (a) limited number of samples measured, 

 (b) contamination of cores by the drilling mud, and (c) loss of cores during the 

 drilling operations. 



The most satisfactory method for measurement of core specimens is the poten- 

 tial drop method discussed in connection with Figure 278. Electrical connection to 

 the ends of the core specimen may be obtained by wrapping a few turns of bare wire 

 tightly around each end at right angles to the axis of the core. Two single turn coils 

 are employed for making connection to the core for measuring the potential drop 

 across any convenient length L. 



