50 OIL-FIELD WATERS IN SAN JOAQUIN VALLEY, CAL. 
of the region, is typically of meteoric origin; that is, it is rain water 
that has entered the ground and dissolved some of the more soluble 
constituents of the rocks. The salt water, however, is typically of 
connate origin and represents sea water that has been entrapped and 
retained in the sediments, dissolving some of their constituents and 
losing some of its own, but in the main retaining its original compo¬ 
sition. The connate water is relatively stationary or stagnant, but 
the meteoric water is to some extent continually descending from the 
surface and mixing with the connate water. Both types are simi¬ 
larly affected by constituents of the oil or gas, sulphate being removed 
and carbonate introduced, but whereas the composition of the mete¬ 
oric water is entirely reversed by this process, the pure connate water, 
which contains at the start only a small proportion of sulphate, is 
much less conspicuously altered. Most waters are mixtures of con¬ 
nate and meteoric types, and the extent of their alteration therefore 
depends on the proportions of the mixture. Two sets of forces are 
at work; the one leads to the mixing of two opposing types of water 
in various proportions, and the other induces in both types chemical 
changes which are similar in kind but different in degree. 
This distinction between meteoric and connate waters is valuable 
in forming a conception of the genetic relations of the oil-field waters, 
but it may be well to reiterate that it can not be strictly applied in 
the field. (See p. 22.) Connate marine water is readily identified by 
its high content of chloride, but the connate fresh water which the 
rocks may contain can not be distinguished from meteoric water. 
Although the terms strictly represent origin, in actual practice they 
are necessarily reduced to a chemical basis and are so used in this 
report. As the reactions of a water with hydrocarbon material depend 
on its chemical character rather than on its origin, the precise genetic 
classification is chiefly of theoretic value. 
An attempt has been made to present graphically the chemical rela¬ 
tions of the oil-field waters in figure 3. In this diagram the meteoric 
water is shown as entering the rocks and percolating down toward the 
oil, undergoing a modification and finally a reversal of its chemical 
character; the connate water is shown as already existing in the 
rocks but undergoing a similar alteration as the oil is approached; 
and the two classes are shown as converging and mixing in various 
proportions. The three broad divisions of both types and their mix¬ 
tures, according to their relation to the oil, may be called normal, 
modified, and altered. Normal ground water is that which contains 
a normal percentage of sulphate; this percentage is generally high, 
for this type is either pure meteoric water or a mixture in which 
meteoric water predominates. Strictly normal or unaltered connate 
water has not been encountered. The modified group, characterized 
by a percentage of sulphate lower than normal, may be either meteoric 
