FPSO – General Overview of Conversion & Topside Process Description

By Anoop Rajendran Nair

Surveyor Registro Italiano Navale (RINA)

Abstract

This paper intends to give a brief insight into the conversion of an Oil tanker to a FPSO mainly emphasizing the process activities in the topside modules of a typical FPSO along with the utility systems present. The content of the paper is on the basis of my past two year’s experience as the RINA attending surveyor for the conversion and commissioning of FPSO Firenze. The major structural components in a FPSO are - Vessel side (either can be a purpose built new one or conversion from old tanker) - Turret side (core of the FPSO by which it is moored, can be forward or in the middle) - Topside process modules (Production, stabilisation & utilities, gas compression, power generation, gas dehydration, H2S removal etc.) The major process activities in the topside modules of a FPSO are: − Receive fluids from subsea wells through the turret piping lines; − Process inlet fluids to separate crude oil from produced water and natural gas; − Dewater and stabilize the crude oil in order to meet the export quality specifications, including maximum H2S content; −Store the stabilized crude oil in dedicated vessel cargo tanks and offloads to the shuttle tankers; − Compress and dehydrate associated gas and sent to the oil wells as lift gas; −Treat the produced Fuel gas for burning in the boiler, gas turbine and flare in order to meet the air emission regulations and to limit the H2S content in the gas; −Treat the produced water in order to meet the regulations for discharging into the sea; The major process systems in a FPSO are as below: - Production manifold - Crude oil separation and treatment - Crude oil stabilisation - Crude oil transport, storage & Offloading - Produced water (treatment & stripping) - Lift gas/ Kick Off gas compression -.Gas dehydration - Fuel gas associated systems - H2S Removal from gas - Chemical injection - Flare, Vent & Blow down

The major utility systems in a FPSO are as below: - Fresh water generation - Sea water for topsides - Compressed air - Nitrogen generation - Antifouling (MGPS) - Drains (open & closed) This paper covers in brief the various components of the systems listed above with their process flow diagrams and respective piping diagrams, so as to provide an idea of the process activities in the topside of a typical FPSO in a sequential manner. The process of removal of H2S from gas is also briefed in this paper which is a rare phenomenon in conventional FPSOs.

Key Words FPSO, Turret, Topside, Process Module, Crude oil, Gas, Produced water, Compression, Separation, Stabilisation, Storage, Offloading, Dehydration, H2S Removal, Sour water, Chemical injection, Fuel gas, Lift gas, Flare, Blowdown, Heater, Drain, Stripping, Utility