Page 272 - Geochemistry of Oil Field Waters

256 CLASSIFICATION OF OILFIELD WATERS

Class 4: d = (a + b)
2a = primary salinity
2b = secondary salinity

Class 5: d > (a + b)
2u = primary salinity
2b = secondary salinity
2(d -a - b) = tertiary salinity (acidity)

These five classes of water are found in nature. Examples of the first three
classes are various surface waters, sea water and brines represent class 4,
while mine drainage waters and waters of volcanic origin fall in class 5
(Palmer, 1911).
Rogers (1917, 1919) studied oilfield waters of the San Joaquin Valley,
California, and used the classification system of Palmer (1911). He found
that generally the surface waters of the San Joaquin Valley possess second-
ary salinity rather than primary alkalinity, contain more sulfate than
chloride, and contain low amounts of bicarbonate. With increasing depth,
the subsurface waters decrease in secondary salinity until primary alkalinity
becomes evident. Waters above an oil zone often contained hydrogen sulfide,
which was attributed to reduction of sulfates by hydrocarbons, thus de-
creasing the amounts of sulfate and increasing the bicarbonate in the water,
which Rogers called an altered water. Further he found that, in these altered
waters in close proximity to hydrocarbon accumulations, chloride becomes
relatively and absolutely important because of the residual chloride from the
original (ancient) sea water chlorides as compared to waters above the oil
zone which often are freshened because of a more hydrodynamic situation.
Altered waters, according to his definition, can have either primary alkalinity
or secondary salinity depending upon their amounts of carbonate and chlo-
ride, but normal waters have only secondary salinity.
Elliott (1953) used the Palmer system to determine the chemical charac-
teristics of some Paleozoic age formation waters in Texas. He found that all
of the waters in the group that he studied (about 70) contained predomi-
nant, primary salinity. Many of these waters contained appreciable concen-
trations of sulfate; one contained 5,800 mg/l sulfate, and many contained
more than 2,000 mg/l. The calcium concentration ranged up to 13,000 mg/l
while the bicarbonate concentrations ranged up to 800 mg/l.
Ostroff (1967) used the Palmer classification to classify waters from
several basins and to compare this classification system with two other
systems. He found that the Palmer system groups some of the constituents
together that are not closely related chemically. Furthermore the system
does not consider ionic concentrations or saturation conditions related to
sulfate or bicarbonate.