Page 242 - Geochemistry of Oil Field Waters

226 ORIGIN OF OILFIELD WATERS

Kramer (1969) did not have these controls because he used only the
published data of various laboratories.
Carpenter and Miller (1969) used statistical and thermodynamic methods
in an effort to determine the origin of the dissolved chemical constituents in
saline subsurface waters in north-central and northwestern Missouri. Statisti-
cal analysis of scatter diagrams indicated that the concentrations of lithium,
sodium, potassium, and bromide and the ion activity ratios of K+/H+,
Ca+’/Mg+*, and Sr+’ /Ba+’ in the waters are influenced by reactions with
constituents in the aquifer rocks. They concluded that the ion ratios are of
little value in determining the origin of the waters because the concen-
trations of the dissolved constituents in the waters had reacted with minerals
in the aquifer rocks. This study was excellent because it did show that the
concentrations of constituents in the water are controlled to some extent by
reactions with the aquifer rocks. Additional work of this kind is needed in
the study of deep brines.
A study of brines from the Sylvania formation in the Michigan Basin
indicated that evaporation and dolomitization were two dominant controls
for their dissolved concentrations of calcium, magnesium, sodium, stron-
tium, and bromide (Egleson and Querio, 1969). Mechanisms responsible for
concentrations of elements such as potassium, lithium, rubidium, ammonia,
boron, and iodide were believed to be reactions with sedimentary rocks,
leaching of organic constituents, and bioconcentration.

Relation to depth and salinity

A study of the chemical composition of some selected Kansas brines
indicated that in general the concentrations of calcium, sodium, and chloride
increase with increasing salinity, while the sulfate concentrations decrease
(Dingman and Angino, 1969). However, the Ca/C1 ratio, concentrations of
calcium and salinity, did not generally increase with geologic age or with
depth of the aquifer.
Dickey (1969) surveyed the analyses of oilfield waters from many areas of
the United States and concluded that in general the Ca/Mg ratio increases
with increasing salinity while the ratio Na/(Ca + Mg) decreases irregularly
with increasing. salinity and depth. This observation is compatible with the
findings of several investigators. The dominant anion in subsurface waters
usually changes with depth; in near-surface waters, it is sulfate; at depths
exceeding 520 m it is bicarbonate; and in deep brines, it is chloride
(Chebotarev, 1964). The Ca/Na ratio usually increases with depth and age of
the associated rocks, while the Mg/Na ratio decreases.

Iodide

Collins (1969a) studied the chemistry of some oilfield brines from the
Anadarko Basin which contain high concentrations of iodide. The concen-