COMPOSITION OF THE OIL-FIELD WATERS. 
91 
fields. This line is oblique to the strike of the beds and the changes 
are therefore more gradual than they would be along a line normal 
to the strike. The total distance is about 18,300 feet, the wells being 
equally spaced. All the waters occur below the top oil sand and are 
believed to come from the same general horizon. 
Complete analyses of the waters are given in Tables 9 and 11 (pp. 74 
and 77). As shown in figure 7, the waters of the two wells near the 
outcrop are primary alkaline, whereas those farther east are brines. 
With distance from the outcrop there is a marked decrease in primary 
alkalinity, which if continued would lead to the total disappearance 
of this property at some point between the second and third wells. 
Distance between wells in feet 
Figure 7.— Diagram showing gradation between waters of the mixed type in the western part of the 
Midway-Sunset field and the brines that occur at the same general horizon in the deeper territory to the 
east. Section extends from SE. \ sec. 31, T. 32 S., It. 24 E., to NE. £ sec. 31, T. 12 N., R. 23 W. 
In the same direction there is a corresponding rise in primary salinity, 
indicating that at some point the water is characterized by only two 
properties. East of this point primary salinity decreases and sec¬ 
ondary salinity appears, rising to 16.2 per cent in the water farthest 
from the outcrop. The concentration curve shows a steady rise with 
distance from the outcrop, and in the distance covered by the figure 
more than trebles. It will be noted that there is much less differ¬ 
ence between the waters of the two wells farthest from the outcrop 
than between those of the two nearest, indicating that beyond a 
certain point the infiltration of meteoric water is negligible. Beyond 
the farthest well the brine shows no further changes and is fairly 
uniform in composition. Between the first well and the outcrop, 
however, the water probably increases rapidly in primary alkalinity 
and near the outcrop passes to the reversed type. 
