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EXPLORATION GEOPHYSICS 



The accompanying figures illustrate (a) the results of the geoelectrical 

 survey and (b) a comparison of these results with available data obtained 

 from subsequent drilling. Figure 351 is a portion of the geoelectrical 

 structure contour map. The group of ten representative wells for which 

 well log information was available are connected by a discontinuous line. 

 At each well location, the well log elevation of the top of the Yates sand 

 is shown opposite the well symbol. The bracketed figure represents an 

 extrapolation of the Yates sand datum to the deeper horizon employed 

 in the geoelectrical correlations. This bracketed figure is directly com- 

 parable, therefore, to the subsurface values that may be interpolated from 

 the geoelectrical structure contour map. 



This comparison is better illustrated by Figure 352 which shows the 

 subsurface values plotted on a discontinuous profile between the wells 

 shown in Figure 351. 



Fig. 352. — Structure profiles showing comparison of geoelectrical survey results with results of 

 subsequent drilling. (East Vacuum Area, Lea County, New Mexico.) 



The survey covered a total area of approximately 200 square miles 

 and required approximately six months for completion.* Subsurface 

 geoelectrical determinations were made over an approximate depth range 

 of 3000 to 5000 feet, at 350 separate stations. 



The geoelectrical survey results were submitted in terms of structure 

 contours and profiles showing the average structural trend in the section 

 included between the top of the Yates sand and the top of the White 

 lime. Because of the generally greater reliability of the deeper geological 

 marks, greater weight was attached to the geoelectrical correlation of the 

 lower part of the measured section. 



The available well log data are for the top of the Yates sand which 

 occurs at a somewhat shallower horizon than that employed in the geo- 

 electrical work. To facilitate the comparisons illustrated in the accompany- 

 ing figures, it was necessary therefore to extrapolate from the Yates 

 sand values, and also to interpolate the geoelectrical values from 

 the nearest geoelectrical station to the location of the check well. 



* A portion of the results only are shown in Figure 351. 



