92 
OIL-FIELD WATERS IN SAN JOAQUIN VALLEY, CAL. 
The belief that this chloride-carbonate water, which is associated 
with the oil in the Westside Coalinga and in the western or shallower 
portion of the Midway and Sunset fields, is in reality a mixture of 
meteoric and connate waters is corroborated by other observations. 
Thus, the average ratios of magnesium to calcium and of sodium to 
potassium in waters of the mixed type are intermediate between those 
in the brines on the one hand and in the chiefly meteoric waters on the 
other. These ratios have been calculated in all the analyses given 
in this report, and the averages for each type are presented in the 
following tables. For the purposes of this comparison it may be 
assumed that all the waters of the normal and modified groups and 
of the reversed type of the altered group are essentially of meteoric 
origin. As practically all these waters contain some of the con¬ 
stituents of connate water, whereas the brines are relatively pure, 
the mixed type would be expected to resemble the essentially 
meteoric waters more closely than the brines. Thus, the average 
ratio of magnesium to calcium in 16 waters of the mixed type is 1.29, 
as against 1.34 in 50 chiefly meteoric waters, and 0.71 in 13 brines. 
Sodium and potassium have been separately determined in only 16 
of the analyses in this report, so that the average ratios are of less 
value. The average sodium-potassium ratio in 6 waters of the 
mixed type is 188, as against 246 in 6 chiefly meteoric waters and 
165 in 4 brines. Although in the deeper waters the individual ratios 
of both magnesium to calcium and sodium to potassium are fairly 
constant, in the upper meteoric waters they show considerable varia¬ 
tion; hence if twice as many analyses were included the figures would 
be somewhat different. That the figures given may fairly be consid¬ 
ered representative, however, is indicated by the writer’s study of a 
large number of analyses not included in this report. 
Average ratios of magnesium to calcium in reacting values in 7.9 analyses of dif¬ 
ferent ty-pes of water from the Coalinga, Midway, and Sunset fields. 
> 
Type of water. 
• i 
Coalinga field. 
Midway-Sunset 
field. 
Both fields. 
Average 
ratio. 
Number 
of 
analyses. 
Average 
ratio. 
Number 
of 
analyses. 
Average 
ratio. 
Number 
of 
analyses. 
Surface water. 
3.08 
2 
0.90 
5 
1.52 
7 
Ground water: 
Normal. 
1.04 
18 
1.35 
4 
1.09 
22 
Modified. 
.90 
4 
1.70 
3 
1.25 
Reversed. 
1.70 
12 
1.65 
2 
1.69 
14 
Brine. 
.90 
1 
.70 
12 
.71 
13 
Mixed. 
1.62 
5 
1.15 
11 
1.29 
16 
Averages: 
All meteoric waters.•_ 
1.35 
36 
1.31 
14 
1.34 
50 
All types. 
1.37 
42 
1.06 
37 
1.23 
79 
