BORE-HOLE INVESTIGATIONS 



1077 



The statistical treatment of the data may be illustrated by a practical 

 instance. Suppose a number of samples from each of several water zones 

 are analyzed. Mean values are calculated from several samples of each 

 zone. Suppose further that the mean value of the ratio of the potassium 

 to sodium content is very different in each of the zones and the deviations 

 from the mean are small, then this ratio is assumed to be diagnostic. It 

 is postulated that by setting up several diagnostic factors, inferences can 

 be drawn regarding the origin of the water zones. 



THE DIPMETER 



In the study of geological structures and in the selection of locations 

 for new wells, it is important to know the angle and direction of the dip 

 of the strata. The dip of the strata may sometimes be determined by the 

 study of mechanical cores, cut under special conditions. Various other 

 methods have been employed, but generally they have met with limited 

 success. 



WINCH 



GALVANOMETERS 



Fig. 671. — Schematic arrangement for logging the spontane- 

 ous potential on three sides of a bore hole. 



Dip Determination between Wells. — Dip measurements are often 

 obtained by correlating the electric logs of at least three wells or drill holes 

 not in a straight line. The correlation lines passing through the same form- 

 ations in the three wells define the plane of the formations. This method 



