42 OIL-FIELD WATERS IN SAN JOAQUIN VALLEY, CAL. 
which is usually the sulphate. As the oil fields on the west side of 
the valley are located in a very arid region the relative prominence of 
the alkalies in the shallower waters is to be expected. Furthermore, 
in connate water (fossil sea water) the alkalies greatly predominate 
over the other bases, and as the deeper oil-field waters are partly 
or wholly of connate origin, two sets of conditions have combined to 
cause the high concentration of alkalies in the waters of the fields 
of the west side. In the Kern River field, on the east side of the 
valley, water is more plentiful, and the first condition is therefore 
less pronounced, but as the deeper waters are partly of connate 
origin their content of alkalies is fairly high. 
In sixteen of the analyses given below sodium and potassium have 
been determined separately. The potassium is generally present in 
very small proportion, the average ratio of sodium to potassium by 
weight being about 125 to 1. The average surface water in most 
regions contains by weight about one-fourth as much potassium as 
sodium, and ocean water only about one-thirtieth as much. 1 This 
discrepancy is due to the fact that when mixed solutions containing 
sodium and potassium are passed through soil or clay the potassium is 
almost wholly extracted and held, whereas the sodium is comparatively 
unaffected; 2 hence the potassium in ordinary surface waters is largely 
lost during their passage to the sea. Similarly,, if sea water is then 
entrapped in the sediments, the separation will continue still further 
and nearly all the potassium will he removed. This principle has 
thus operated to remove nearly all of the potassium in the connate 
and partly connate water of the oil fields. (See p. 93.) 
Alkaline earths (calcium and magnesium ).—In a few of the surface 
waters and shallow ground waters in the oil fields of the west side 
of the valley the alkaline earths exceed the alkalies, but in practically 
all the deeper waters their relative proportion is very low. This is 
due not only to the high concentration of the alkalies, as already 
explained, but also to the fact that the alkaline earths themselves 
are generally present in small actual amount. Large amounts of 
the earths can not be retained in waters in which more than a cer¬ 
tain value of carbonate or bicarbonate is present, and if this value 
is exceeded alkaline earth carbonates are precipitated from the solu¬ 
tion. In most of the shallower waters sulphate is high and carbonate 
low, and alkaline earths are therefore important constituents, but 
in the waters near the oil zone in the western parts of the Coalinga, 
Midway, and Sunset fields carbonate is high and the earths are 
accordingly low. In the connate waters in the central part of the 
Midway and Sunset fields chloride is very high and carbonate low, 
1 Clarke, F. W., The data of geochemistry, 3d ed.: U. S. Geol. Survey Bull. 61G, p. 138, 1916. 
2 Van Bemmelen, J. M., Das Absorptionsvermogen der Ackererde: Landw. Versuchs-Stationen (Ber¬ 
lin), vol. 21, pp. 135-191, 1878. 
