108 OIL-FIELD WATERS IN SAN JOAQUIN VALLEY, CAL. 
or absence of these substances in a water may serve to determine 
whether the water is from a horizon very near the oil zone or far 
above it, but the validity of such a distinction obviously depends 
on the ease and rapidity with which the water can dissolve the 
acids from the petroleum. If top water leaking down behind the 
casing and mixing with the oil can dissolve petroleum acids before 
it is pumped out such a distinction would be entirely misleading. 
It is probable that the chemical character of the water has much 
to do with its ability to dissolve the acids. In refining oil the 
naphthenic acids are usually removed by the addition of caustic 
soda, for the alkali salts of these acids are readily soluble in water. 
The alkaline-earth salts of the naphthenic acids are somewhat less 
soluble. Hence, when alkali carbonate water of the type associated 
with the hydrocarbons in many parts of the San Joaquin Valley 
fields is brought in contact with oil containing petroleum acids it 
may be inferred that alkali naphthenates or soaps will readily form 
and go into solution. The oil-field brines, however, contain no 
alkali carbonates and only small quantities of alkaline-earth car¬ 
bonates, and the rapid formation of organic salts in these waters 
would probably be less common. In washing the ether solutions of 
the acids Holde x uses a concentrated solution of sodium sulphate in 
order to avoid dissolving the acids. As the acids are thus prac¬ 
tically insoluble in strong solutions of sodium sulphate, and as. 
most of the shallower oil-field waters are essentially solutions of 
sodium sulphate and chloride, it seems probable that brief contact 
of a shallow water with the oil would not suffice for the solution 
of these organic compounds. 
It may therefore be inferred that alkali carbonate waters which 
occur near the oil zone or which have been mixed with the oil before 
being raised to the surface, are most likely to contain salts of the 
petroleum acids; that brines may or may not contain these com¬ 
pounds, and that normal top waters rarely contain them unless they 
have been allowed to stand in contact with the oil for some time. 
When oil stands exposed to the air, as in a sump, it is probable that 
naphthenic acids are formed by oxidation; hence most sump water, 
especially if it be of the alkali carbonate type, probably contains 
petroleum acids. Water which has been intimately mixed with oil 
in the form of an emulsion is also more likely to contain them. For 
these reasons it would seem that the value of petroleum acids as 
indicators of the original position of a water with respect to the oil 
zone is open to question. The rapidity with which they are extracted 
by different types of water must be investigated before their evidence 
can be positively relied on. 
1 Holde, D., and Mueller, E., The examination of hydrocarbon oils, p. 232, New York, 1915. 
