Page 145 - Geochemistry of Oil Field Waters

Chapter 5. SIGNIFICANCE OF SOME INORGANIC CONSTITUENTS
AND PHYSICAL PROPERTIES OF OILFIELD WATERS

In general, the concentrations of the constituents in various natural solids
of reservoir rocks must be considered along with the amounts that are found
in associated oilfield waters. Some possible chemical reactions between host
rock and reservoir water may deplete or enrich the concentration of the
constituents in oilfield waters. Another important factor is the solubility of a
constituent.
The ionic potential, determined by dividing the ionic radius by the va-
lence, influences the solubility of elements. For example, elements with low
ionic potential are more likely to remain in true ionic solution. Elements
commonly found in oilfield waters have the following ionic potentials:
sodium, 0.95; calcium, 0.50; magnesium, 0.33; chlorine, 1.81; bromine,
1.95; and iodine, 2.16. Apparently the cation (magnesium) and the anion
(chlorine) would be the most likely to remain in true ionic solution; how-
ever, several other variables occur during diagenesis which lead to depletion
or enrichment of constituents in waters.

Lithium
Lithium is the lightest alkali metal; it has a distinctly smaller radius,
0.60 8, than the other alkalies and is the smallest of all singly charged
cations. It is one of the less abundant elements, and its abundance in the
earth’s crust is about 6.5 x wt.% (Fleischer, 1962). Here again, it is an
exception because in general, the lighter elements tend to be more abundant
than the heavier elements. It is lithophilic in that it tends to be associated
with the silicate phase in rocks (Ahrens, 1965); however, because of its small
size, it supposedly cannot replace the abundant alkali metals in mica.
It and the other alkali metals exist in a uniform positive one state of
oxidation and are inherently ionic. Their chemical behavior depends almost
entirely upon electron loss, and their chemistry is simpler than that of any of
the other metallic elements (Moeller, 1954).
Lithium is potentially toxic to plants (Hem, 1970), yet it is regularly
found in plant ashes, which indicates that it normally is present in soil waters
(Goldschmidt, 1958). Coal ashes of Neurode, Silesia, contained up to 198
ppm lithium, whereas soils in northeast Scotland contain 30-5,000 ppm.
The content of lithium in sediments ranges up to 6 ppm in quartzites and
sandstones, up to 15 ppm in calcareous rocks, and up to 120 ppm in clays
and shales.