Oil and gas production handbook An introduction to oil and gas production

deaerator is used to reduce oxygen in the water before injection. Oxygen 
can cause microbiological growth in the reservoir. The deaerator is designed 
to use strip gas and vacuum. 
8.7.3  Ballast water 
Ballast systems are found on drilling rigs, floating production ships, rigs and 
tension leg platforms (TLP). The object is to keep the platform level at a 
certain depth under varying conditions, such as mode of operation 
(stationary drilling, movement), climatic conditions (elevation of rig during 
storms), amount of product in storage tanks, and to adjust loading on TLP 
tension members. 
 
Ballasting is accomplished by means 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. 
 
If fresh water is produced, it 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 at sea. 
8.8 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 2,000 liters (500 gallons) of antifoam can be used. At a cost of 2 € per 

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liter, ($10  per gallon) in bulk, antifoam alone will cost some 4,000 € or 
$5,000 per day. 
 
The most common chemicals and 
their uses are: