Oil and gas production handbook - Process Control and ...

The ballasting is accomplished by way of ballast tanks, pumps and valves, which are
used in combination with position measuring instruments and tension force meters
(TLP) to achieve the desired ballasting.
Produced water, if available can be used as ballast to avoid salt water. Additionally,
if ballast water has become contaminated from oil tanks, it must be cleaned before
discharge to sea.
5.7 Chemicals and Additives
A wide range of chemical additives are
used in the main process. Some of these
are marked in the process diagram. The
cost of process chemical additives is
considerable. A typical example is
antifoam where a concentration of about
150 ppm is used. With a production of
40.000 bpd, about 2000 litres (500
Gallons) of antifoam could be used. At a
cost of 2 /liter, 10 $/Gallon in bulk, just
the antifoam will cost some 4000 Euro /
5000 USD per day.
The most common chemical s and their uses are:
Scale inhibitor
Emulsion breaker
The well flow contains several different contaminants such
as salts, chalk, and traces of radioactive materials. As
pressure and temperature changes, these may precipitate and
deposit in pipes, heat exchangers, valves and tanks. As a
result these may clog up or become stuck. The scale
inhibitor will prevent the contaminants from separating out.
Scale or sediment inhibitor is added on wellheads and
production equipment.
Water and Oil cannot mix to form a solution. However
small drops of oil will disperse in water and small water
drops will disperse in oil. These drops are held suspended
by attractive and repulsive electrostatic forces at the
molecular level. This is called an emulsion and will form a
layer between the oil and water. Although the emulsion
layer will eventually break down naturally, it prevents full
74