Page 117 - Petroleum and Gas Field Processing

3.8 SELECTIONS AND PERFORMANCE OF
GAS–OIL SEPARATORS

For the selection of a particular separator, preliminary survey of all
conditions and factors prevailing on site in an oil field should be
considered. The main factors underlying this survey as well as the basic
steps included in the selection of a separator are embodied in one
integrated scheme outlined in Figure 26.
The performance of gas–oil separators, on the other hand, are
controlled by four factors:
1. Operating temperature: A higher temperature will cause more
evaporation of the hydrocarbons, diminishing the recovery of
the liquid portion. In general, the trend of change in the relative
volume of the liquid recovered from a GOSP with temperature
is illustrated in Figure 27.
2. Operating pressure: A higher pressure will allow more
hydrocarbons to condense, increasing liquid recovery. However,
after reaching a certain peak, a higher pressure causes liquid to
decrease [4]. This is in accordance with the retrograde
phenomena explained by Abdel-Aal [3]. In Figure 28, the
lower curve V s represents this case.
3. Number of stages: Increasing the number of stages in general
will increase the efficiency of separation, resulting in a higher
yield of the stable stock tank oil. This is true for a number of
stages in the range of two to three. However, if the number
increases beyond three, improvement in the recovery diminishes.
A four-stage GOSP is not economically attractive, as the
recovery of stable stock tank oil increases by 8% by adding one
more stage [8].
4. In addition to the above factors, the composition of the well
streams has to be considered in evaluating the performance of a
gas–oil separator.
In order to judge the performance of a GOSP, a number of tests are
commercially carried out to evaluate the efficiency of operation. Most
important are the following:

1. Evaluation of particle size: The method requires determining the
size of liquid particles entrained by the gas stream. The efficiency
of gas–oil separator is thus evaluated based on this size. It is
accepted that liquid particles with size larger than 10 mm coming
in the gas stream is an indication of poor performance.

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.