392 



Subsurface Geologic Methods 



Figure 175. Comparison of an electrical log and core record in a section composed 

 of oil sand, salt-water-bearing sand, and shale (Texas Tertiary) . 



diameter; however, as shown in figure 163, the resistivity is a function of 

 bed thickness, which becomes of major importance for thicknesses close to 

 that of the electrode spacing. These factors must be taken into considera- 

 tion when true resistivities are determined. 



The foregoing discussion shows clearly the potential value of the 

 correct use of an electric log. Experiments and research are being carried 

 out today that will soon make possible a more complete evaluation of true 

 resistivity and therefore an even more thorough formation study. The 

 electric log is much more than merely a correlation tool, and with a 

 complete understanding of the factors influencing the log much valuable 

 information may be obtained. 



