Summary
A major challenge in offshore development is to ensure unimpeded flow of
hydrocarbons. Managing solids such as hydrates is the key to the viability of
developing a deepwater prospect. Common methods to prevent and reduce hydrate
risks are generally based on injection of thermodynamic inhibitors to prevent
hydrate formation, or use of kinetic hydrate inhibitors to sufficiently delay
hydrate nucleation/growth. Currently, the amount of inhibitor required is
either calculated and/or determined based on lab experiments. The amount of
inhibitor depends on various parameters, including, water cut, inhibitor loss
to hydrocarbon phases, aqueous and non-aqueous fluid compositions, operating
conditions. Generally, a safety factor is considered and the resulting
inhibitor is injected upstream without much downstream measurements. Despite
the usual safety margins, gas hydrates are formed, which could result in
serious operational and safety concerns. This is mainly caused by changes in
the system conditions (e.g., rates and water cut) and/or malfunction of the
equipment. In most cases, the amount of inhibitor is more than necessary and is
not adjusted with seasonal changes, affecting CAPEX/OPEX.
As a result of a joint industry project, several novel techniques, based on
downstream and online measurements, have been developed. These techniques could
be divided into the following categories:
- Monitoring hydrate safety margin to optimize inhibitor injection rates. The
system determines the amount of inhibitor in the aqueous phase and the degree
of inhibition they can offer.
- Detecting initial hydrate formation, as an early warning system against
hydrate blockage. The system detects the changes in the system caused by
hydrate formation with the aim of giving the operator enough time to prevent a
blockage.
The main advantages of these techniques include minimizing the amount of
inhibitor required and preventing pipeline blockages caused by hydrates, hence
the cost of inhibitor; impact on the environment; cost of remedial actions; and
deferred production. A number of techniques have been investigated during this
project, with some techniques selected for prototype development. The developed
prototypes have been tested in the project sponsors' laboratories and some in
commercial production. In this paper, an update on the latest results of this
new approach in flow assurance control is presented.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
4 February 2008
- Meeting paper published:
5 May 2008
- Revised manuscript received:
16 September 2008
- Manuscript approved:
19 September 2008
- Published online:
5 March 2009
- Version of record:
5 March 2008
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