Page 273 - Geochemistry of Oil Field Waters

SULIN’S CLASSIFICATION 257

Sulin’s classification

Sulin (1 946), a Russian geochemist, proposed a classification system based
upon various combinations of dissolved salts in the waters. The waters are
described according to chemical type, subdivided into group, subgroup, and
class. He found four basic environments of natural water distribution:
(1) Continental (terrestrial) conditions which promote the formation of
sulfate waters. Such conditions supply soluble sulfate constituents to the
water and the genetic type of such a water is “sulfate-sodium”.
(2) Continental conditions which promote the formation of sodium bicar-
bonate waters. The genetic type is “bicarbonate-sodium ”.
(3) Marine conditions and the formation of a “chloride-magnesium ” type
of water.
(4) Deep subsurface conditions within the earth’s crust and the formation
of a “chloride-calcium ” type of water.
The first two types are characteristic of meteoric and/or artesian waters,
the third of marine environments and evaporite sequences, and the fourth of
deep stagnant conditions.

Types, groups, and subgroups

Water composition is expressed in milligram-equivalents of the separable
ions, and the composition is calculated per 100 g of water. The percent of
the sum of the equivalents is used to exclude the degree of water mineraliza-
tion, and to compare waters containing different amounts of dissolved solids.
The ratio Na/Cl expressed in the percent equivalent form determines the
genetic water type. If the value is greater than one, sodium predominates
over chloride and the excess sodium can be combined with sulfate or bicar-
bonate. Therefore waters with a Na/Cl ratio greater than one belong to the
bicarbonate-sodium or the sulfate-sodium types. Sulin calculated sodium as
the sum of all the alkalies (Li, K, Na etc.) and chloride as the sum of all the
halides (Cl, Br, I).
The ratio (Na - C1)/S04, if greater than one, indicates that the water is
the bicarbonate-sodium type, while if it is less than one it is the sulfate-
sodium type. Similarly the ratio (Cl- Na)/Na if less than one indicates the
chloride-magnesium type, but if greater than one it indicates the chloride-
calcium type.

Water classes

Subdivision of the groups of waters were made by Sulin (1946) using the
Palmer (1 911 ) characteristics, because these characteristics express the dis-
solved constituents in the waters in a generalized format. For example, the
sum of the alkali chlorides and sulfates corresponds to primary salinity, and
the sum of the alkaline earth chlorides and sulfates corresponds to secondary