Slug Catchers in Natural Gas Production - NTNU

Karam – Slug Catchers in Natural Gas Production
mainly due to the inability to determine minutely the velocity and the flow regime under which the
pipe is operating especially as counter-current flow is frequent and unpredictable in mltiphase flow.
The diameter of the fingers is determined at a minimum to ensure a stratified flow and then increased
to maintain the same flow regime at the inlet of the buffer. Similarily, a downward inclination of the
fingers ensure a stratified flow.
The dimensions of the slug catcher, based on the method stated in this paper, might be larger than
needed. This is due the volume of accumulated liquid assumed to be lower than the calculated volume
as the liquid keeps on being under the gas bubbles in the liquid film during production. The
operational liquid holdup used is the one prior to production while in reality this value is lower due to
gas pockets and film production. Nevertheless, an overestimation of the slug catcher can be considered
as a safety factor for production. The calculations are also flexible and can be applied to more than one
finger as long as symmetry is maintained.
HYSYS simulator has been used to generate models reflecting the amount of gas, water and
condensates. The models are not reliable due to the numerous simplifications assumed and the
difficulty in simulating multiphase flow. Multiphase flow is accurately represented by the OLGA
simulator which was not available in the HYSYS package I have been using due to a limited license.
The simplified HTFS homogeneous flow correlation has been used for pipe and well calculations.
Many of the input data were also assumed due to the lack of information which makes it difficult to
create a model operating as the real field. The steady state flow is assumed throughout the entire
production.
Ormen Lange model is the most accurate model among the four fields due to the availability of data
and due to symmetry in the field design which makes its modeling precise. As for the rest, either some
of the main input data such as the elevation profiles were missing or the wells are not located
symmetrically or at the same distance from the PLEM. Further assumptions regarding those two
matters made it hard to rely on the HYSYS outcome.
The slug option provided by the HYSYS has shown that some of the results have been affected by the
injection of the MEG and the length of the bubbles as well as that of the slug were reduced. The
amount of MEG injected based on the sheet provided by the Hydrate Engineering book was 49 wt%
which is lower than what is currently used in the field (~ 60 wt%). This is mainly due to the inputs to
the sheet which are taken from the HYSYS simulator. Furthermore, the volume of water expected to
Page 30 of 56