94 OIL-FIELD WATERS IN SAN JOAQUIN VALLEY, CAL. 
and in other fields. Hofer 1 mentions this widespread peculiarity of oil¬ 
field waters and presents a compilation of 27 analyses of sulphate- 
free water from various fields in Europe, Asia, and North America. 
However, neither Hofer nor, so far as the writer knows, any other 
writers on this subject have attempted to work out the chemical 
relations of the various types of water in any one field, hut present 
merely isolated analyses of “oil-field water,” the position of which 
with regard to the oil is generally not stated. The waters differ 
widely in chemical composition, some of them being concentrated 
brines very high in secondary salinity and others closely resembling 
the mixed (carbonate) type found in the San Joaquin Valley fields. 
The mixed type is less common but appears to be characteristic of 
the Russian and Galician fields. The nearly pure alkali carbonate 
water (reversed type) found in the Eastside Coalinga field has appar¬ 
ently not been found elsewhere. Some of the analyses show unusually 
large amounts of iodine and bromine, and several other rare elements 
have been reported, but the common characteristic of all the waters 
examined is the absence of sulphate. In some waters this is so com¬ 
plete that barium salts have been found in the solution. 2 
The earlier investigators apparently regarded these sulphate-free 
waters more as chemical curiosities than as normal and reasonable 
phenomena, but the absence of sulphate has since been attributed to 
the reducing action of the hydrocarbons. The reaction between sul¬ 
phate and organic matter was suggested by Bischof 3 to explain the 
origin of certain sulphur deposits. It is supposed that the sulphate 
is reduced to sulphide, which passes off as hydrogen sulphide, and 
that an equivalent portion of the oil or gas is oxidized to carbon 
dioxide and carbonate. Hofer writes the reaction substantially as 
follows: 
CaS0 4 + CH 4 = CaO + H 2 S + C0 2 + H 2 0 
or 
CaS0 4 + CH 4 = CaS + C0 2 + 2H 2 0 = CaC0 3 + H 2 S + H 2 0 
These reactions, however, are hypothetic and are open to several 
objections. It has long been known that sulphate solutions are 
decomposed under some conditions in the presence of organic matter 
with the formation of hydrogen sulphide. 4 It was shown by Meyer 5 
and more definitely by Plauchud, 6 however, that this decomposition 
1 Engler, C., and Hofer, H., Das Erdol, Band 2, p. 28, 1909. 
2 Idem, p. 28. 
3 Bischof, G., Chemische und physikalische Geologie, 2, pp. 144-164,1851. 
4 Lersch, B. M., Hydro-chemie, pp. 235-238, Berlin, 1864. Clarke, F. W., The data of geochemistry, 
3d ed.: U. S. Geol. Survey Bull. 616, p. Ill, 1916. 
5 Meyer, Lothar, Chemische Untersuchung der Thermen zu Landeck in der Grafschaft Glatz: Jour, 
prakt. Chemie, Band 91, pp. 5-6, 1864. 
3 Plauchud, E., Recherches sur la formation des eaux sulfureuses naturelles: Compt. Rend., vhl. 84, p. 
235, 1877; Sur la reduction des sulfates par les sulfuraires, et sur la formation dessulfures metalliques, 
naturels: Idem, vol. 95, p. 1363,1882. Etard, A., and Olivier, L., De la reduction des sulfates par les 
gtres vivants: Idem, vol. 95, p. 846, 1882, 
