6 
OIL-FIELD WATERS IN SAN JOAQUIN VALLEY, CAL. 
1. Oil-field water is not necessarily salty, as is generally believed, 
and may not be even slightly salty to the taste. The degree of concen¬ 
tration of chloride in such water is governed primarily by local condi¬ 
tions and is not affected by the position of the water in relation to oil. 
2. Sulphate, which predominates in most of the shallow ground 
waters on the west side of San Joaquin Valley, diminishes in amount 
as the oil zone is approached and finally disappears. 
3. The concentration of carbonate increases as the oil zone is 
approached but depends largely on the concentration of chloride. 
4. The horizon, with respect to the oil zone, at which these altera¬ 
tions take place, is different in each field. 
On the basis of these conclusions, which appear to be well grounded, 
at least for the area studied, the following practical suggestions may 
be made: 
In drilling a well in untested territory it may be possible to obtain 
an indication of the presence or absence of oil and gas below by ascer¬ 
taining by analysis whether the sulphate is diminishing and the car¬ 
bonate increasing in the waters successively encountered. In some 
areas a significant change may be detected as much as 1,000 feet 
above the oil; in others the upper limit of alteration may be within 
a few hundred feet of the oil. 
The source of the water in a well that produces a mixture of water 
and oil may be determined, at least in a general way, by studying 
its chemical composition. In the Westside Coalinga field, for exam¬ 
ple, the source of the water may thus be determined rather definitely; 
in the Midway-Sunset field, where the distinctions are less sharp, the 
success of this method will depend largely on the number of authentic 
analyses that are available for comparison. 
In this report the writer aims first to present the evidence on which 
the foregoing conclusions are based and to discuss the interpretation 
of water analyses and their value from the operator’s standpoint, and 
second, to discuss the chemical relations of water and oil in so far 
as present information permits. It is hoped that this preliminary 
presentation will indicate the importance of experimental geochemical 
work on the interaction of the organic constituents of oils and the 
inorganic substances found in the oil-field waters. Enough is known 
already to warrant the belief that systematic experimental work in 
petroleum hydrology will yield results of practical as well as scientific 
value. 
ACKNOWLEDGMENTS. 
The writer wishes to express his appreciation of the assistance and 
cooperation rendered by Mr. R. W. Pack, with whom he was asso¬ 
ciated in a study of the Midway and Sunset fields for the United 
States Geological Survey during the summer of 1914. Dr. Chase 
Palmer and Mr. Herman Stabler, also of the Survey, as authors of 
