Page 30 - Geochemistry of Oil Field Waters

Chapter 3. ANALYSIS OF OILFIELD WATERS FOR SOME PHYSICAL
PROPERTIES AND INORGANIC CHEMICAL CONSTITU-
ENTS

Water analyses are used by the petroleum industry in studies related to
subsurface formation identification, pollution problems, water compatibili-
ties, corrosion, water-quality control, waterflooding, and exploration.
Efforts to standardize methods applicable to analyzing oilfield waters have
been made by the American Petroleum Institute (1968), and currently
similar efforts are being made by the American Society for Testing and
Materials.
The methods discussed in this chapter include wet chemical procedures
for calcium, magnesium, barium, carbon dioxide, sulfide, sulfur compounds,
selenium, oxygen, spent acid, fluoride, chloride, bromide, and iodide. In-
strumental methods are described for pH, Eh, specific gravity, resistivity,
suspended solids, acidity, alkalinity, oxygen isotopes, ammonium nitrogen,
phosphate, boron, arsenic, copper, nickel, lead, manganese, zinc, cadmium,
and silica. Also described are emission and atomic absorption methods for
lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, barium,
manganese, zinc, copper, iron, and lead; and emission spectroscopic methods
for aluminum, beryllium, boron, iron, manganese, and strontium. ._
The methods used to analyze oilfield waters should be capable of producing
precise and accurate results. Methods applicable to analyzing fresh waters
may or may not be directly applicable to a petroleum-associated water, but in
general such a method will need modification or complete redevelopment
because the petroleum-associated water contains a more complex and con-
centrated array of dissolved salts than the fresh water.

Quality control

Data provided by the analytical laboratory are used in decision-making,
and the data must describe precisely and accurately the characteristics or
concentrations of the constituents in the sample. Usually an approximate or
incorrect result is less valuable than no result because it leads to faulty
interpretations.
The analyst needs to be aware of his responsibility to provide results that
reliably describe the sample. Further, he should know that the procedures
that he uses, his professional competence, and his reported values may be
used or challenged. To meet any challenge his results must be adequately