Page 159 - Geochemistry of Oil Field Waters

BARIUM 147

170 ppm; and secondary gypsum, up to 1,100 ppm (Goldschmidt, 1958).
Sea water contains about 8 mg/l of strontium, but subsurface brines contain
up to 3,500 mg/l. Fig. 5.11 is a plot of chloride versus strontium content for
some subsurface brines taken from some Tertiary, Cretaceous, and Jurassic
age sediments. Most of these samples were enriched in strontium compared
to the evaporite-associated water, and it is possible that a mechanism similar
to dolomitization could cause the enrichment. In comparison to calcium, the
strontium appears to be increasingly accumulated; for example, only five
samples (from Tertiary sediments) fell within the normal evaporite curve.
Fig. 5.12 is a similar plot for some subsurface brines showing similar results
taken from sediments of Mississippian and Pennsylvanian age.

Barium

Barium, like strontium, is a minor element, comprising 0.04 wt.%, of the
earth’s crust; it is more concentrated in igneous rocks and less concentrated
in sedimentary rocks (Fleischer, 1962). It, like the other alkaline earth
metals, is predominantly lithophile. Table 5.111 illustrates some of the
properties of barium; its ionic radius, 1.35 A, permits it to replace potas-
sium, but usually not calcium and even less commonly magnesium. Barium
forms more of its own minerals than does strontium. Barium is readily
absorbed by colloids, like potassium, and is therefore retained by soils or
precipitated with hydrolysates; it is also concentrated in deep-sea manganese
nodules (Hem, 1970).
Barium dissolves as bicarbonate, chroride, or sulfate during weathering
processes, and migrates in aqueous solutions as these compounds. The
solubility of barium sulfate increases when hydrochloric acid or chlorides of
the alkali or other alkaline earth metals are present in solution. The proper-
ties of barium are similar to those of strontium. Both precipitate through
loss of carbon dioxide from a bicarbonate-bearing solution, or as sulfates by
the action of sulfuric acid, sulfides, or sulfates. Strontium, however, is less
likely to be absorbed by clays than barium, because its ionic radius is smaller
and its ionic potential is higher.
Encrustation deposits taken from plugged pipes of waterflood systems for
secondary recovery of oil, where barium is present, usually contain barium,
calcium, strontium, iron, and traces of other metals. Barium may cause
problems in waterflood systems by reacting with the chromate-type oxygen-
corrosion inhibitors, forming water-insoluble barium chromate.
The amount of barium found in sandstones, shales, and carbonates is
about 180, 450, and 90 ppm, respectively (Goldschmidt, 1958). Sea water
contains about 0.03 mg/l, and subsurface brines may contain more than 100
mg/l; however, many brines contain less than 10 mg/l. Davis and Collins
(1971) found that 59 mg/l of barium sulfate is soluble in a synthetic brine
with an innic strength of 3.0487, containing sodium, calcium, magnesium,