Page 262 - Origin and Prediction of Abnormal Formation Pressures

234 H.H. RIEKE, G.V. CHILINGAR AND J.O. ROBERTSON JR.

free alkaline bases, which is a result of the hydrolytic action of water on dissolved
weak acid salts. Dissolved ions in water are divided into three groups: (1) soluble
alkalies (sodium, potassium, lithium); (2) meagerly soluble alkaline earths (magnesium,
calcium, strontium, barium); and (3) hydrogen, whose salts are acids and cause acidity
(Collins, 1975).
Palmer's classification system uses the sum of the reacting values (capacity for
reaction) of the individual ionic species in each group to define five classes based on five
special properties of water. Reacting values are calculated in percent by summing the
milliequivalents of all the ions, then dividing the mequiv of a given ion by the sum of
the total mequiv and multiplying by 100. The predominance of reacting values in each
group is the basis for the special properties, which are:
9 Primary salinity (alkali salinity), which does not exceed twice the sum of the reacting
values of the alkali radicals.
9 Secondary salinity (permanent hardness) is defined as the excess of any salinity over
primary salinity and does not exceed twice the sum of the reacting values of the
alkaline earth group radicals.
9 Tertiary salinity (acidity) is any excess of salinity over primary and secondary
salinity.
9 Primary alkalinity (permanent alkalinity) is any excess of twice the sum of the
reacting values of the alkalies over salinity.
9 Secondary alkalinity (permanent alkalinity) is the excess of twice the sum of the
reacting values of the alkaline earth group radicals over secondary salinity.
The Palmer classification system has some shortcomings, such as the grouping of
some of the constituents together that are not closely related chemically, and it does not
consider ionic concentrations of saturation conditions related to sulfate or bicarbonate.
(For additional details see Collins, 1975.)

Sulin's classification
Sulin (1946) devised a classification system based upon various combinations of
dissolved salts in water and tied it to the environmental origin of the water. The sulfate-
sodium water groups are indicative of terrestrial conditions, bicarbonate-sodium water
groups represent continental conditions, chloride-magnesium water groups form under
marine conditions, and the chloride-calcium groups are related to deep subsurface
conditions.
The water classification scheme of Sulin consists of: (1) genetic water types estab-
lished by value of the Na/CI ratio; (2) chemical types using values of the ratios of
(Na-C1)/SO4 and (CI-Na)/Mg; (3) groups subdivided based on Palmer's characteristics
as determined by the classes; (4) classes depending on Palmer's salinity or alkalinity
values; and (5) subgroups established using the Ca/Mg and SO4/C1 ratios. Sulin consid-
ered sodium as the sum of Na, Li, K ions, and chlorides as the sum of C1, Br, and I. The
classification system is completed by determining the sum of the milligram equivalents
per 100 g of water (indicator of water mineralization).
The Sulin's class subdivision scheme employs the distinction of whether or
not sodium bicarbonate is present. In the sulfate-sodium, chloride-magnesium, and
chloride-calcium water types there is no sodium bicarbonate present.