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Test Separators and Well test
Test separators are used to separate the well flow from one
or more wells for analysis and detailed flow measurement. In this
way, the behavior of each well under different pressure flow
conditions can be determined. This normally takes place when the
well is taken into production and later at regular intervals, typically
months and will measure the total and component flow rates under
different production conditions. Also undesirable behavior such as
slugging or sand can be determined. The separated components are
also analyzed in the laboratory to determine hydrocarbon
composition of the Gas oil and Condensate.
The test separator can also be used to produce fuel gas for
power generation when the main process is not running. In place
of a test separator one could also use a three phase flow meter to
save weight.

Production separators
The main separators are gravity type. On the right you see
the main components around the first stage separator. As
mentioned the production choke reduces will pressure to the HP
manifold and First stage separator to about 3-5 MPa (30-50 times
atmospheric pressure). Inlet temperature is often in the range of
100-150 degrees C. On the example platform, the well stream is
colder due to Subsea wells and risers.
The pressure is often reduced in several stages; here three
stages are used, to allow controlled separation of volatile
components. The purpose is to achieve maximum liquid recovery
and stabilized oil and gas, and separate water. A large pressure
reduction in a single separator will cause flash vaporization
leading to instabilities and safety hazards.
The retention period is typically 5 minutes, allowing the
gas to bubble out, water to settle at the bottom and oil to be taken
out in the middle. In this platform the water cut (percentage water
in the well flow) is almost 40% which quite high. In the first stage
separator, the water content is typically reduced to less than 5%.

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