CHEMICAL RELATIONS BETWEEN WATER AND HYDROCARBONS. 93 
/rNa\ 
Average ratios of sodium to potassium in reacting values i \ 
Coalinga, Midway , and Sunset fields. 
in 16 waters from the 
Average 
ratio. 
Chiefly meteoric water 
Mixed type. 
Brine. 
Average of all types... 
246 
188 
165 
204 
Number of 
analyses. 
. 6 
6 
4 
16 
CHEMICAL RELATIONS BETWEEN WATER AND THE 
HYDROCARBONS. 
ALTERATION OF WATERS BY THE HYDROCARBONS. 
NATURE OF ALTERATIONS. 
It has been shown that the waters associated with the oil in the 
San Joaquin Valley oil fields are almost or quite sulphate-free, not¬ 
withstanding the fact that the shallower waters of the region are 
characterized by a large concentration of sulphate. An equally 
striking feature of many of the waters associated with the oil is the 
presence of alkali carbonate, which is lacking in the shallow waters 
on the west side of the valley. Between the sulphate and carbonate 
zones is a zone characterized by waters carrying hydrogen sulphide. 
Outside the oil fields sulphate and carbonate maintain the same 
mutual proportions to great depths and hydrogen sulphide waters 
are rare; the conclusion is therefore irresistible that a change in the 
composition of the oil-field waters has been caused directly or indi¬ 
rectly by constituents of the oil or gas. As sulphate is abundant in 
the shallower waters everywhere on the west side of the San Joaquin 
Valley, whereas sulphide is found only near the hydrocarbons, it is 
reasonable to suppose that the sulphide has been derived under special 
conditions through reduction of the sulphate. In regions where sul¬ 
phates are rare or only locally distributed the alternative hypothesis— 
that sulphide has accompanied the oil from below and that sulphate 
is formed by its oxidation—may have to he considered, but as this 
condition does not prevail in the oil fields of San Joaquin Valley this 
hypothesis need not be discussed. 
REDUCTION OF SULPHATE. 
The observation that waters associated with oil contain no sulphate 
is by no means new, for it was pointed out in 1882 by Potiiitzin 1 that 
the waters associated with oil in the Caucasian oil fields contain no 
sulphate, and this has been amply confirmed by later workers there 
i Potiiitzin, A., Zusammensetzung des die Naphta begleitenden und aus schlammvulkanen ausstro- 
menden Wassers (abstract): Deutsche chem. Gesell. Ber., Band 15, p. 3099-b, 1882. 
