78 OIL-FIELD WATERS IN SAN JOAQUIN VALLEY, CAL. 
entered into their composition. Broadly considered, the first factor 
is a function of the depth, hut the second depends on structural con¬ 
ditions and is therefore a function of the geographic position. In 
figure 4 these two factors can not well be distinguished, and therefore 
in the following sections several groups of analyses are presented in 
which the two lines of variation may be studied separately. 
VERTICAL RELATIONS. 
Analyses 74 to 77, Table 12, represent four waters occurring in the 
southwestern corner of the Westside Coalinga field. The samples 
were collected at different times from four wells, and are therefore 
not as satisfactory as if taken from one well. However, the four 
wells are located within 1,200 feet of a central point, and as the water 
sands appear to be persistent within this area the four waters may 
be considered as occurring in the same well. Analysis 74 represents 
water from a depth of about 800 feet, and may include some water 
from a sand at 600 feet. Analysis 75 represents a water that corroded 
the casing at 1,160 feet; its exact position is not reported in the log, 
but a study of the logs of neighboring wells reveals a persistent 
water sand which would occur in this well at about 1,100 feet, and 
which is doubtless the source of this water. Analysis 76 represents 
water from a depth of 1,347 feet, or below the tar sands and about 
250 feet above the oil, and No. 77 is the “bottom water” which occurs 
25 feet below the main oil zone. It will be noted that Nos. 74 and 
75 are secondary saline waters of the normal group, and that Nos. 
76 and 77 are primary alkaline waters. No. 76 may be referred to 
the modified group and No. 77 to the mixed type of the altered 
group. The sulphate salinity ratio decreases from 80 per cent in the 
highest water to 0.6 per cent in the lowest and the ratio of carbonate 
to sulphate increases from 0.05 in the highest to 90.5 in the lowest. 
In order to show the relations of these waters graphically the four 
analyses have been plotted in figure 5, A, as though they represented 
waters occurring in the same well. The vertical scale shows the dis¬ 
tance in feet between the water sands and the oil zone. On the hori¬ 
zontal lines representing the water sands are plotted the percentages 
of the radicles in reacting values and the concentration of the water 
in parts per 5,000, and the points thus obtained are connected by 
lines to show the variations of each constituent. A glance at the 
figure is sufficient to show that the most marked changes take place 
near the zone of tar sands or between the second and third waters; 
the two upper waters are very similar and the lowest differs from the 
third chiefly in its higher chloride. The heavy line representing 
sulphate shows the most pronounced and regular variation, decreas¬ 
ing from 38 per cent in the highest water to 0.2 per cent in the lowest. 
