Jee determined the size and routes of subsea three pipelines required to develop three gas fields outside the UK, using the local national design code.
These are two 323.8 mm (12in) by 33 km and 21 km long lines containing untreated well fluids, and a 404.6 mm (16in) by 17 km long export gas line.
This preliminary front-end engineering design (FEED) study used preliminary reservoir and platform process information to determine the diameter, wall thicknesses and concrete weight coating for the three lines linking one manned two and normally-unmanned platforms to deliver the export gas to a tie-in on an existing line to shore.
The investigation examined the stability of the seabed sediments in
the area, the need for trenching and likelihood of self burial.
At the client’s request, the bulk of the conceptual study was
completed within the first three weeks, with further clarification of
the design in the following few weeks.
The front-end engineering conceptual design study also included
- development of the Basis of Design (BoD) document including determination of seabed sediments, metocean data and abstracted flow regime (temperature and pressures)
- optimisation of diameters for flows over life of the fields
- determination of the temperature gradient envelopes of the lines and expansion potential in the buried and unburied state
- optimisation of the diameter of the lines throughout the life of the development
- slugging flow in the flowlines and risers, determined using PipeSim software
- suitability of carbon steel and determination of the required corrosion allowance
- report the legal requirement for buried lines
- determination of the magnitude of trawling interaction loads that could be applied to surface lines
- recommendation of concrete thickness for installation using S-lay and the revised steel thickness for reel-lay barge. This ensures the pipelines will remain stable during installation and operation
- determine propensity for lateral buckling and minimum burial cover to prevent upheaval buckling
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