Page 90 - Geochemistry of Oil Field Waters

78 ANALYSIS OF OILFIELD WATERS

Reagents. The necessary reagents are:
(1) Sodium solution: see reagents preparation under “Potassium”.
(2) Standard barium solution: obtain commercially or dissolve 1.5161 g of
BaClz in 1 liter of water. 1 ml of this solution contains 1,000 pg of barium.

Preliminary calibmtion. Prepare standard barium solutions containing 2-1 0
pg/ml of barium using the standard barium solution and 50-ml volumetric
flasks. Add to each of these and to a blank, 0.5 ml of the sodium stock
solution. Aspirate these standards and the blank as recommended in the
calcium method and determine the absorbance at a wavelength of 5336 8.

Procedure. Transfer an aliquot of brine to a 50-ml volumetric flask. The
specific gravity of the brine can be used as a guide in estimating the size of
an aliquot containing about 0.1 mg of barium. Add 0.5 ml of the sodium
stock solution, dilute to volume with water, and aspirate. Calculate the
approximate sample concentration from the preliminary calibration readings
and determine the aliquot size that will contain about 0.1 mg of barium.
Transfer equal aliquots containing about 0.1 mg of barium to three 50-ml
volumetric flasks. Add no barium standard to the first flask, 0.1 mg of the
barium standard to the second flask, and 0.2 mg to the third. Add 0.5 ml of
the sodium stock solution to each of the three flasks and dilute to volume.
Aspirate and record the absorbance readings for each sample.

Calculations. See calculations under “Lithium” in the flame spectrophoto-
metric section, Fig. 3.3 or Table 3.XI:
mg Ba x 1,000
ml sample = mg/l Ba+’
Precision. In a single laboratory using oilfield water samples containing con-
centrations of 7 and 8 mg Ba+’/l, the standard deviations were k0.5 and
kO.9, respectively. The recoveries were 108.2% and 97.3% respectively.

Manganese

Manganese is determined at the 2794.8 8 wavelength with an air-acetylene
flame.

Reagents. The necessary reagent is a standard manganese solution: obtain
commercially or dissolve 1.000 g of manganese in a minimum volume of (1
+1) nitric acid. Dilute to 1 liter with 1% (v/v) HC1.l ml of solution contains
1 mg of manganese.

Preliminary calibration. Prepare standard manganese solutions containing
1-5 pg/ml using the standard manganese solution and 50-ml volumetric
flasks. Aspirate these standards arid a blank as recommended in the calcium
method, and determine the absorbance at a wavelength of 2794.8 8.