Case History

Subsea Production System Decommissioning

Overview

A FPSO in the East coast of India was expected to shut down after years of service. All related system was required to be thoroughly cleaned out of hydrocarbons, gas and deposits (e.g. sluge, scale and NORM) before it could sail to a yard for refurbishment.

SANCCUS was appointed to provide chemical solutions to this decommissioning project.

Solution

Intro

Structures

There were 4 x 8" Production Risers (PR1, PR3, PR2 & PR4) to be cleaned/deoiled and 4 x 8" Gas Export Risers (GE1, GE2, GE3 & GE4) and 1 x 6" Gas Injection Riser (GIR) to be cleaned/degassed.


Deoiling Risers

Step 1

Gel Train was pumped down to PR1 in the order of Aqualink Gel, Sandstorm 1, Aqualink Gel, J-Clean 1 and Aqualink Gel. Propelled by treated seawater, it was then pumped up to PR4.


Deoiling Risers

Step 2

Repeat the same process with PR2 and PR3. The riser contents were routed to the slop oil tanks via the FPSO separators.


Degassing Risers

Step 3 & 4

Gel Train was pumped down to GE1 in the order of Aqualink Gel and J-Clean 1. Propelled by treated seawater, it was then pumped up to GE4. The same process was repeated with GE2 and GE3.


Degassing Riser

Step 5

Gel Train was pumped down to GIR in the order of Aqualink Gel and J-Clean 1. The riser contents were routed down to the Gas Injection Well.


Flushing Flowlines

Step 6

The infield flowlines were decommissioned by opening the Xmas Tree and Production Manifold valves in sequence to drive the flowline contents with seawater down to the Production Wells.


Final Check

Step 7

The system is filled with seawater, isolated and depressurised to ambient pressure.

Result

Approx. 30km of risers were effectively treated to meet the following specifications:

  1. <1% LEL of methane
  2. <40ppm oil in water
  3. Comply with industrial standards (e.g. for NORM and Mercury)
  4. Made ready for preservation

Value

SANCCUS Gel Train methodology enabled multiple cleaning operations in one go.

If it was done purely with the treated seawater, it would have taken much longer to meet the above specifications. The operation was a great success and reinforced the industry's confidence in the effectiveness of gels.

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Scotland, UK

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