Page 270 - Geochemistry of Oil Field Waters

254 CLASSIFICATION OF OILFIELD WATERS

Portions of three classification systems (Palmer, 1911; Sulin, 1946;
Schoeller, 1955) and Bojarski’s (1970) modification of Sulin’s system were
applied to about 4,000 formation waters (U.S. Bureau of Mines, 1965). The
waters were analyzed by standard methods (American Petroleum Institute,
1968). The results indicated that the classifications are useful in exploration
and production problems.

Palmer’s classification

Palmer (1911) observed that the basic characteristics of natural waters are
dependent upon their salinity (salts of strong acids) and alkalinity (salts of
weak acids). Salts that cause salinity are those that are not hydrolyzed, while
alkalinity is caused by free alkaline bases produced by the easily hydrolyz-
able salts of weak bases.
All positive ions (cations) including hydrogen can cause salinity, but of
the negative ions (anions), only the strong acids, (e.g., chloride, sulfate, and
nitrate) can cause salinity. Because salinity is dependent upon the combined
activity of the cations and anions and is limited by the reacting values of the
strong acids, its value is determined by multiplying the total value of the
strong acids by two.
Alkalinity is caused by free alkaline bases as a result of the hydrolytic
action of water on dissolved bicarbonates and other weak acid salts. The
alkalinity value is calculated by doubling the reacting values of the bases
which exceed the reacting values of the strong acids.
The ions that commonly are found in waters comprise three groups: (a)
alkalies (sodium, potassium, lithium), whose salts are easily soluble in water
and do not cause hardness; (b) alkaline earths (magnesium, calcium, stron-
tium, barium), whose salts cause hardness and many of which are sparingly
soluble; and (c) hydrogen, whose salts are acids and cause acidity.
Geologists know what “strong alkalies”, “alkaline earths”, “strong acid
radicles”, “weak acid radicles”, “ions”, and “reacting values” mean general-
ly. To compare several analyses it usually is easier if they are made on a
chemical basis. The. proportions of the various ions do not react in propor-
tion to the various weights given in milligrams per liter but rather in propor-
tion to their “capacity for reaction”, or “reaction value”. The reacting value
of each ion is determined by multiplying the amount of each radicle by
weight (mg/l) by its “reaction coefficient”, which is the valence of a radicle
divided by its atomic weight.
The groups of the ions are determined by summing the reacting values of
their members, and according to the predominance of reacting values of the
groups, five special properties were designated by Palmer. To determine the
special properties, the reacting values of a group of cations or anions are
doubled so that the full value of a given special property is considered. The
terms “primary” and “secondary” were used to qualify the general proper-