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Flow Assurance for Offshore Pipeline

Flow assurance, by definition, focuses on the whole engineering and production life cycle from the reservoir through refining, to ensure with high confidence that the reservoir fluids can be moved from the reservoir to the refinery smoothly and without interruption. 

The full scope of flow assurance is shown in Fig. 1. Flow assurance matters specific to subsea tieback systems are shown in Fig. 2. Flow assurance is sometimes referred to as “cash assurance” because breakdown in flow assurance anywhere in the entire cycle would be expected to lead to monetary losses. A few specific flow assurance issues are discussed next.

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  Fig. 1—Full scope of flow assurance (courtesy of MSL Engineering).
  
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  Fig. 2—Flow assurance matters for subsea tieback systems (courtesy of BP).
  

Flow assurance is required to determine the optimum flowline pipe size based on

reservoir well fluid test results for the required flowrate and pressure. As the pipe size

increases, the arrival pressure and temperature decrease. Then, the fluid may not reach

the destination and hydrate, wax, and asphaltene may be formed in the flowline. If the

pipe size is too small, the arrival pressure and temperature may be too high and

resultantly a thick wall pipe may be required and a large thermal expansion is expected.

It is important to determine the optimum pipe size to avoid erosional velocity and

hydrate/ wax/asphaltene deposition. Based on the hydrate/wax/asphaltene appearance

temperature, the required OHTC is determined to choose a desired insulation system

(type, material, and thickness.) If the flowline is to transport a sour fluid containing H2S,

CO2, etc., the line should be chemically treated or a special corrosion resistant alloy

(CRA) pipe material should be used. Alternatively, a corrosion allowance can be added

to the required pipe wall thickness. capital expense (Capex) and operational expense

(opex) using CRA, chemical injection, corrosion allowance, or combination of the above

should be exercised to determine the pipe material and wall thickness.

Fig 3 shows various plugged flowlines due to asphaltene, wax, and hydrate

deposition.

Sources:

http://petrowiki.org/Flow_assurance_for_offshore_and_subsea_facilities

Lee, Jaeyoung. 2007. Introduction Offshore Pipeline and Risers.