26 OIL-FIELD WATERS IN SAN JOAQUIN VALLEY , CAL. 
sand lenses or by structural barriers. The very fact that the oil 
itself can accumulate and remain within a small area under high 
pressure for long periods of time implies that the underground 
circulation is decidedly restricted. Hence if salt water originally 
saturated the beds it is reasonable to expect that under most condi¬ 
tions some of it would be retained also. No very positive proofs of 
this simple explanation can be offered until more is known of the 
chemical character of oil-field waters in relation to physical condi¬ 
tions, but in the absence of evidence to substantiate the theory that 
chlorides are concerned in the formation of the oil, this suggestion 
may be worthy of consideration. 
Another view that may be mentioned in passing is that salt water 
in oil fields has certain peculiarities of composition which indicate 
that it is, in part at least, of deep-seated origin. 1 It has been shown 
that the distribution of salt water in the San Joaquin Valley oil 
fields may be explained on simple physical principles, and it will be 
shown below that this water has nearly the composition of sea water 
with certain modifications due to definite chemical reactions. There 
is nothing to show that it has emanated from the interior of the earth, 
and an appeal to recondite agencies is unnecessary. 
DISTRIBUTION OF WATER IN THE OIL FIELDS. 
The following notes on the occurrence of water in the several oil 
fields are included in order to enable one unfamiliar with the fields to 
understand more clearly certain features of the chemical relations of 
the waters. No attempt is made to describe local conditions in 
detail or the damage wrought by the intrusion of water into the oil 
sand. Most of the analyses on which this paper is based represent 
waters from the Coalinga, Midway, and Sunset fields, and reference 
to the physical conditions in these fields will again be made in dis¬ 
cussing the chemical relations of the waters. 
COALINGA FIELD. 
The Coalinga oil field is divided into two fairly distinct districts, 
the Westside and the Eastside fields. The Westside field is situated 
on the western limb of a syncline and the Eastside field is practically 
confined to the summit and eastern limb of the anticline to the east. 
The deeper portion of the syncline has not been explored. The 
ground-water level in the whole area is generally within 200 feet of 
the surface, and most of the water needed for industrial use is 
obtained from comparatively shallow water wells. Throughout the 
area the shallower waters are highly mineralized and are notable for 
their very high proportion of sulphate. 
1 Washbume, C. W., Chlorides in oil-field waters: Am. Inst. Min. Eng. Trans., vol. 48, pp. 687-094, 1915. 
