Changing Design Criteria of FPSO's Based on Computational Fire Simulation
Authors: Mendes M.F. , França M.A.S. , Araújo M.S. 
Published: October 2008

Oil production using Floating Production Storage and Offloading (FPSO) installations is an irreversible trend in the oil industry. However, the risks associated with storage and production are more than the simple sum of those from a production platform, an oil tanker ship and an offloading terminal.

This paper presents and discusses some of the results obtained with one of the most critical of those risks: a fire accident. Based on computational fire simulation, it was analyzed how fire accidents affect offshore installations and how its results modified the final layout of some giant FPSO's. Significant results, obtained in the last 10 years of analysis, are discussed for Semi-submersible and Fixed Platforms, FSO and FPSO's, with process plants ranging from 15,000 to 200,000 b/d.

Introduction

Due to their capabilities of production and storage in a single vessel, allied to reduce construction costs, FPSO's look like one of the best solution for shallow and deep waters. In the past 10 years, the number of oilfields using FPSO's has shown a tremendous growth around the world.

Giant oilfields in Africa and South America are operating based on FPSO's with production capacity up to 200,000 b/d and storage of 2,000,000 barrels. They are installed at water depths ranging from 160 to 1,350 m.

There are almost 80 FPSO operating or in construction now in the world. A small number if compared with the 4,000 platform and 3,000 oil tankers (above 6,000 gt), but FPSO's concentrate a significant production capacity.

Only in Brazil, 6 FPSO (~ 8 % of offshore production installations) and 2 FSO now are operating, dealing with 800,000 b/d, or almost 60% of the total Brazilian oil production. Their storage capacity ranges up to 11,000,000 barrels. PETROBRAS has confirmed more 2 FPSO's for Barracuda &Caratinga field and some others operators are planning more 4.

However, there are some concerns about this kind of installation that results directly from their benefits. The first one is the pollution potential associated with a large leakage, which can threat areas even far away from the field. The second is the difficult to fight emergency accidents at Cargo Tanks, like fires, due to some characteristics that will be discussed on this paper.

The search for a solution to those concerns requires a perfect understanding on how those risks can occur and what are the basic causes.

Large oil spills can be caused by external causes, outside the tanks, like collisions, fires, explosions, loading / unloading process, mooring fails, storms, human errors and others. Fires at Cargo Tanks have been reported [1] on Oil Tankers Ships, some of them during their trips, at the sea.

Considering the potential risks associated with fires, it was decided to analyze this kind of risk with a comprehensive methodology, using specific tools that are normally outside the scope of typical Quantitative Risk Analyses (QRA).

The main purpose of fire simulation is to improve the final layout design, increasing the strength to fire accidents and reduce associated frequency.