CASE STUDIES

UPSTREAM FACILITY CONSIDERATIONS

The Split FLNG concept can be adapted to a wide range of applications by selecting a host facility suitable for the site specific gas composition, water depth, metocean conditions, well drilling and intervention method, condensate storage & handling, etc.  Host facilities that have been considered for various cases including:

  • FPSO – circular, spread moored
  • FPSO – ship shape, turret moored
  • Fixed Platform – conventional or self-installing
  • Concrete Gravity Base Platform (GBS)
  • Tension Leg Platform
  • Production Semi-submersible

Case studies using three different upstream host facilities are discussed further.

DEVELOPMENT CASE STUDIES

Timor Sea – Australia

The Timor Sea lies between northern Australia and New Guinea and contains several discovered, but undeveloped gas fields in WD ranging from 300 – 500 ft.  The metocean conditions are moderate, punctuated with seasonal tropical cyclones.  Gas compositions are typically lean with low condensate yields, but with high CO2 content, typically > 12 mole percent.

A conventional fixed steel jacket was selected for the host facility to provide a cyclone resistant, stable wellhead platform for drilling and production with a separate, larger fixed platform for gas processing. The wellhead platform handles basic separation and depletion compression. A 2-level integrated gas treatment platform provides the following gas processing functions for 300 MMSCFPD:

  • Primary & Secondary Membranes for bulk CO2 removal to < 3%
  • Amine Unit for final acid gas removal
  • Mole Sieve dehydration
  • Mercury Absorption Beds
  • Turbo-expander for hydrocarbon dewpointing
  • Fractionation Tower for separation of residue gas from CO2 after Secondary Membrane

The 1.5  MTPA liquefaction vessel is designed as described previously, except that a used 138,000 m3 Moss carrier is converted.   The liquefaction vessel would disconnect from the turret and evacuate the field in advance of an approaching cyclone.   A semi-submersible provides both accommodation and tender support for platform drilling operations.

Browse Basin  – Western Australia

A concept was investigated for dry gas fields in 2500 – 4000 ft. WD offshore W Australia.  The metocean conditions are moderate to severe with 100 year cyclone winds = 105 knots (1 hr.) and Hs = 55 ft.  Gas compositions are typically lean with low condensate yields, but with high CO2 content, typically > 12 mole percent.

A TLP was selected for the host facility to provide cyclone resistant, stable platform for gas processing and well completion/workovers . Gulf of Mexico experience shows that TLP’s are proven for withstanding tropical storms in these water depths.  The TLP hull has 4 x 62 ft. OD columns on 203 ft. spacing with 100 ft. draft.  These dimensions are similar to deepwater Gulf of Mexico TLP’s.

The TLP hull and topsides would be would be mated at the fabrication yard and dry towed to a nearby port.  The 2-level integrated topsides  provides the following gas processing functions, arranged in 1 train x 300 MMSCFPD, sufficient for 2 MTPA.

  • Primary & Secondary Membranes for bulk CO2 removal to < 3%
  • Amine Unit for final acid gas removal
  • Mole Sieve dehydration
  • Mercury Absorption Beds
  • Turbo-expander for hydrocarbon dewpointing
  • Fractionation Tower for separation of residue gas from CO2 after Secondary Membrane
  • Amine unit for acid gas removal

TLP hull sizing is sensitive to topsides weight, so wells would either be pre-drilled using a MODU or drilled from the TLP using Tender Assist Drilling.  The 2  MTPA liquefaction vessel is designed as described previously based on a new build 155K m3 DFDE ship.   The liquefaction vessel would disconnect from the turret and evacuate the field in advance of an approaching cyclone.   A semi-submersible provides both accommodation and tender support for platform drilling operations.