Twister Supersonic Separator

Sub-sea processing

sub-sea-processing.jpg Its breakthrough simplicity makes Twister the missing link for sub-sea gas processing. Twister BV and FMC completed a feasibility study in 2002 to investigate the feasibility of the Twister technology for sub-sea field application. No show-stoppers were identified, although several components included in such a sub-sea processing plant need further development and qualification prior to installation and operation on the seabed. Twister BV, FMC and various other partners have secured an EU subsidy for a four year development programme which will result in the design, construction, installation and testing of the first pilot Twister sub-sea gas processing installation. A joint technology development co-operation agreement was signed with Petrobras in 2006 to develop a sub-sea gas processing system using Twister technology. Twister BV will ship a Twister module to Petrobras in January 2008. This unit will be started up mid-2008 and will be used by Petrobras for gaining operator experience. The second phase of the agreement is expected to kick off during early 2009 and will comprise a sub-sea test on the Canapu field in a water depth of 1600 metres.

Benefits of sub-sea Twister

Twister dehydration and dewpointing enables dry, single-phase export, eliminating many flow assurance risks and limitations associated with wet, multiphase export systems.

Benefits of sub-sea gas conditioning may include:

  • Improved hydraulic performance of pipeline:
    The pressure drop in a single-phase pipeline can be significantly lower compared to single phase gas export and easier to predict. The pressure drop across the Twister process (25-35%) may be more than compensated by the reduced pressure drop in the export pipeline. Twister may also allow a lower pipeline design pressure. Slug prevention: by splitting the flow into separate single-phase gas and condensate streams, terrain or ramp-up induced slugging is prevented and costly slug-catchers may be avoided. Routine pigging for liquid hold-up management, a costly and inherently hazardous operation, can be avoided. Multi-phase export also limits both pipeline turndown flexibility and maximum pipeline size, sometimes necessitating multiple smaller diameter pipelines and often eliminating the flexibility to tie-in future developments.
  • Hydrate prevention:
    MEG supply lines and regeneration facilities can be eliminated. The chemistry of the produced, saline formation water in combination with the hydrate inhibition chemicals may result in operational problems such as chemical degradation and scale depositions. Costly vacuum glycol desalination facilities may be required to manage glycol salt contamination and associated operational and corrosion issues.
  • Corrosion prevention:
    Twister will be a particularly attractive option for corrosive services which may necessitate a CRA export line, i.e. for gas compositions with a CO2 fraction in excess of 4 mol%. Effective corrosion management for wet gas CS pipelines will normally require routine pigging to maintain a protective chemical film on the inside wall of the pipeline. This requirement is costly and cumbersome for subsea developments.
  • Reduced cost:
    Opportunities for pipeline savings where tie-in to an existing export pipeline is possible (e.g. hot tapping).
  • Improved performance:
    Opportunities to de-bottleneck offshore/onshore processing facilities by subsea gas conditioning.