Page 250 - Geochemistry of Oil Field Waters

234 ORIGIN OF OILFIELD WATERS

1,000 -
000 -
600 - A Louisiana
- Mississippi
400- A Alabama
0 Arkansas
0 Texas
- 200 -
w
\
:
100:
LL 00-
2 60-
0
40 -
20 -

BORON, mg/l
Fig. 7.10. Relationships of the concentrations of chloride to boron in an evaporite-
formed brine to oilfield brines taken from the Smackover formation in five states of the
United States.

Mineral formation
A study of some brines taken from Devonian age reservoir rocks indicated
that dolomitization probably is the most important mechanism in deter-
mining the calcium, strontium, and magnesium content of these brines
(Egleson and Querio, 1969). It also was concluded that the relative amounts
of ammonium, iodide, and lithium in these brines were too high to be
derived directly from sea water, and the ammonium and iodide probably
were enriched in the brines as a result of bioconcentration and subsequent
leaching of organic debris.
Dolostone deposits owe their origin to hypersaline brines (Friedman and
Sanders, 1967). Some dolomite, including diagenetic and epigenetic forms,
originates from subsurface brines. In the geologic columns in several oil-

TABLE 7.XVI

Approximate sea-water composition before and after gypsum precipitation (mg/l)

Io n Before precipitation After precipitation
Calcium 390 0
Magnesium 1,300 1,300
Bromide 65 65
Sulfate 2,580 2,580