634 Subsurface Ceologic Methods 



140 feel. The dip in tlie original well increases with depth, indicating 

 that it is approaching salt; it is expected then that dips in the sidetrack, 

 also approaching the dome, may be higher than in the original hole and 

 that the sand section. A, is practically vertical. The net thickness of the 

 sand in the sidetrack on this basis is the same as in the original well, al- 

 though the apparent thickness is 330 feet. 



The use of the dipmeter in the solution of other problems near 

 piercement domes is shown further in figure 332. A dipmeter survey on 

 well 2 showed that the dip increases from 6° or less east at 3,400 feet 

 to 37° east at 9,700 feet. This condition indicates a thinning section west- 

 ward with the possibility of pinchout traps or accumulation against the 

 dome. This is verified by the short sections in well 1 compared with those 

 in well 2 and by the long sections in well 3 compared with those in well 2. 



The dip increase with depth is believed to indicate again an approach 

 to the salt; the dip thus may be expected to flatten laterally as well as 

 vertically away from the dome, or conversely to steepen near the dome. 

 Correlation of well 2 with well 1, which encountered salt at about 6,800 

 feet, shows a steeper dip than that indicated by the dipmeter survey in 

 well 2. The dip obtained by correlation of well 2 with well 3 is less than 

 that shown by the dipmeter. The lower dip obtained by correlation be- 

 tween wells 2 and 3 and the higher dip by correlation between wells 1 

 and 2 compared with those on the dipmeter are normal and could have 

 been foreseen on the basis of the dipmeter record in well 2, 



The steepening dip westward and flattening eastward are important 

 too in planning further development. The productive reservoir at 9,700 

 feet in well 2 might be considered to be near water, if the steep dip shown 

 thereon was continuous; additional wells to the east, however, coulA be 

 drilled and the reservoir extended if the dip flattens. Well 3 verifies this 

 latter conclusion. 



Correlation is often difficult in areas of steeply dipping beds such 

 as those near piercement-type salt domes and on steep structures in other 

 areas. The problem is further complicated if angular unconformities are 

 present. The correlation of electric logs taken in wells 1, 2, and 3 in 

 figure 333, for example, is not readily apparent. The formation B in well 

 2 might be correlated with D in well 3, or even with F, assuming a fault 

 between the two wells. Likewise, the correlation of B and D in well 2 

 with similar beds in well 1 is not obvious, owing to the lengthened sec- 

 tion in well 1 below the unconformity. The problem is further compli- 

 cated by changes in the appearance of the electric log due to lateral varia- 

 tions of the formations. 



A dipmeter survey in well 3 indicated dips of 30° to 37° S. 67° W. 

 at depths of 1,035, 1,242, and 1,540 feet. These data made possible cor- 

 rect correlations of well 3 with wells 1 and 2 lying to the southwest in 

 the direction of dip. The correlation reveals a truncation of Pennsylvanian 

 beds against the overlying Permian. The dip value obtained by correlation 



