COMPOSITION OF THE OIL-FIELD WATERS. 
55 
origin show a somewhat lower percentage of secondary salinity hut 
a fairly high proportion of sulphate, and therefore fall to the right 
of and somewhat below the surface waters. The waters closer to the 
oil measures,- being lower in sulphate and higher in carbonate, fall 
still farther in the same direction, which is indicated by an arrow. In 
the lower right-hand corner of the chart are the altered waters of 
meteoric origin, forming the reversed type. In the course of their 
progressive alteration from the surface downward these meteoric 
waters therefore fall along a line extending diagonally across the 
whole chart. Their concentration is never high, although the deeper 
waters naturally contain more dissolved mineral matter than those 
near the surface. 
The alteration of the connate waters proceeds in the same direction 
but along another course. For purposes of comparison an analysis 
of ocean water (analysis 52) has been plotted, and it will be noted 
that all of the oil-field brines fall below it and somewhat to the right, 
indicating a loss of sulphate and a decrease in secondary salinity. 
Analyses 25 and 87 may be regarded as intermediate and as repre¬ 
senting modified connate waters. The concentration of all these 
brines is fairly uniform, being close to that of sea water. As sug¬ 
gested by the length of the arrows, the amount of alteration under¬ 
gone by the connate waters in their transition to the brine type is 
very small as compared with the almost complete reversal of com¬ 
position undergone by the meteoric waters. 
Between the chiefly meteoric waters and the chiefly connate fall 
the various mixtures. Only four analyses of normal and modified 
waters of distinctly mixed origin are available, but in the group of 
altered waters variously proportioned mixtures are common. Nearly 
every gradation from typical brine to the practically pure carbonate 
water represented by analysis 36 is shown. The concentration shows 
a similar gradation from more than 15,000 parts per million in the 
brines to less than 5,000 parts in waters of the reversed type. 
SURFACE WATER. 
Representative analyses of surface water from the Coalinga, 
Midwav, and Sunset fields are shown in Table 1. Although these 
waters differ widely in some respects, all of them except No. 6 have 
certain fundamental properties in common. It will be noted that 
in all of them, except No. 6, the sulphate salinity ratio is over 80 per 
cent and that all of them are characterized by secondary salinity. 
In a?l of them the primary salinity is 50 per cent or less, the secondary 
salinity between 15 and 70 per cent, and the secondary alkalinity 
between 11 and 62 per cent. In other words the alkaline earths 
exceed the alkalies and sulphate is generally the predominating acid 
