Oilfield Water Chemistry
Oilfield water chemistry is
almost completely different than water or wastewater treatment.
Many areas need to be addressed when discussing water in the oilfield.
Some areas include: 1) microbiological growth, 2) water injection, 3)
water production, 4) scaling, 5) demulsifying water/oil, 6) corrosion,
7) oil concentration in water, and many more.
Chemicals are used to
control, remove, or prevent problems with any of the aforementioned
areas. Common areas that immediately are of issue to the
consulting chemist are:
15) Total Suspended Solids (TSS)
16) Total Dissolved Solids (TDS)
18) Dissolved Oxygen
19) Inorganic Gases (H2S,
20) Oil Concentration
21) Microorganisms (APB, SRB)
An example as to the
importance of these issues, I will explore the general importance of pH.
The pH measurement is a
logarithmic concentration measure of the 'acidity' or 'basicity' of
hydrogen ions or hydroxyl ions present in water. A pH of 7 is
neutral, while a pH of 1 is highly acidic, and a pH of 14 is highly
basic. The concentration of acid is 10 times stronger at a pH of 5
than at a pH of 6.
When the pH measurement is
taken for oilfield water, and the pH is below 7, there is cause for
alarm. At an example pH of 4, there are usually a relatively high
concentration of sour gases (H2S and CO2).
These acid gases form corrosion products such as the dangerous chemical
Iron Sulphide. Iron Sulphide is dangerous when there is no
moisture around at room temperature, and it is exposed to atmospheric
air. The Iron Sulphide will, literally, spontaneously combust.
No flame is needed to cause a fire.
Also, H2S reacts
with iron from the wall of the pipes to form Iron Sulphide. This
is the corrosive portion of the acid gas at a pH below 7. If left
untreated with chemicals, eventually enough iron will be removed to thin
the pipeline to cause a rupture and possibly a spill.
To prevent this problem from
occurring, and the negative environmental impact, corrosion inhibitors
are periodically injected and the fluids monitored with iron, manganese,
and coupons. This will determine the effectiveness of the
inhibitor, and will be a proactive approach to preventing pipeline
Due to the importance and
frequent need for corrosion inhibitors, Eugene has added several
calculations to his chemical programs to assist in accurate dosing in
the oilfield. See the
Computer section of this website.