Page 42 - Geochemistry of Oil Field Waters

SUSPENDED SOLIDS 31

Eh = E + voltage of reference electrode
Eh= +300+242=+542

However, if the millivolt reading is -300, then:

E = +0.242 - 7.6 x (t - 24)
Note: the calculations for Eh are correct only if the temperature of the
brine is 25OC at the time of measurement. If the temperature is not 25"C, a
correction should be made. For example, the potential of the saturated
calomel electrode is 0.246 V at 20°C and 0.238 V at 30°C. The following
formula can be used to obtain the correct potential:

E = +0.242 - 7.6 x (t- 24)
where t is in degrees Celsius.

Suspended solids

Various inorganic and organic materials are found in petroleum-associated
water. Knowledge of the composition of such material is useful in deter-
mining the source of the material and what treatments can be used to
remove it or prevent it from recurring. Such material may be particles of
oxides of the metals from well casings, pumps, or precipitates caused by
oxidation of the formerly reduced species, such as iron or manganese. Other
suspended solids may be silt, sand, and clay.
An estimation of the amount of material in suspension can be ac-
complished by using a turbidimeter (Rainwater and Thatcher, 1960). This is
done by comparing the intensity of light passing through the solution with
the Tyndall effect produced by lateral illumination of the solution with the
same source of light.

Turbidimeter
Instruments for the measurement of turbidity employ principles of design
related to transmission or reflectance of light. The lack of a primary standard
for turbidity, however, has resulted in a complete absence of uniformity
among the available instruments. Further, the Jackson candle turbidimeter,
which does not depend upon the use of a primary standard, is a primitive
instrument, subject to many interferences, and the measurements generally
are not reproducible.
Recently developed turbidimeters often use for calibration a suspension of
formazin permanently embedded in a cylinder of Lucite. These instruments
produce reproducible readings up to 40 Jackson candle units (JCU), and
samples containing turbidities in excess of 40 JCU should be diluted to