1116 



Subsurface Geologic Methods 



of such apparent-resistivity curves gives valuable depth information. This 

 method is particularly well suited to location of the water table. 



By maintaining a fixed electrode separation and taking observations 

 along a traverse line, a resistivity map may be constructed. This method 

 is applicable to a number of mining problems such as the location of 

 ore bodies, faults, and vein extensions. Figure 591 illustrates an appli- 



FiGURE 592. "Eltran" survey at Sandy Point oil field, Brazoria County, Texas. Pro- 

 ducing wells shown as solid circles. (After Rosaire. Reproduced permission 

 Geophysics.) 



cation to oil prospecting. An experimental survey was made of the 

 Monument oil field in Lea County, New Mexico, using the fixed-spacing- 

 resistivity method. A fixed spacing of 6,000 feet was maintained between 

 power electrodes, and potential measurements were made at selected inter- 

 vals between the power electrodes. The resistivity survey was designed to 

 map the contact at the base of the red-beds section with the anhydrite and 

 salt lying immediately beneath. The red beds are relatively good con- 

 ductors of electricity while the anhydrite and salt are almost insulators. 

 By using existing well data and applying corrections for the lateral 



