Collision Risks Associated with FPSOs in Deep Water Gulf of Mexico
Authors: MacDonald Ali , Cain Michael , Aggarwal Rajiv K. , Vivalda Claudia , Lie Olav E. 
Published: October 2008

In the event of a collision between a vessel and an offshore installation (whether passing or in-field), given the likely volumes of oil that could be released, the possibility for large scale loss of life, asset and environmental catastrophe exists. This paper provides an overview of the ship/platform collision risks and presents the methodologies that can be applied to quantify the frequency and consequences of these events. Particular focus is placed on application of risk assessment methodologies to offshore platforms located in the Gulf of Mexico. This is being demonstrated through a JIP on "Risk and Reliability of a FPSO in Deepwater Gulf of Mexico."

Following an introduction, the paper focuses on three main collision scenarios, which from North Sea experience tend to present greatest threat to an installation. A historical review of each of these collision scenarios is presented and an overview of risk assessment methodologies is provided for the two scenarios most likely to result in pollution, loss of life and asset, and production loss/delay. Measures that have potential to reduce the risk of ship collision are highlighted. Finally recommendations are made for future developments in this area, which could reduce the risk of pollution, fatality and loss of asset.

This paper draws on a large amount of experience developed from research and analysis work performed in the North Sea.

Introduction and Background

Designated shipping fairways for vessels approaching ports and navigating between various ports are provided in the U.S. Gulf of Mexico (GOM). These fairways are located in water depths up to 200m (660 ft). Beyond this, the routes followed are based on the shortest distance from entry to the GOM to the most appropriate shipping fairway.

The fixed platforms in the GOM are designed for protection against collisions from in-field supply vessels by provision of rubber fenders on boat landings and barge bumpers at the platform legs. The assessment of risk from passing vessel collisions and offloading tankers is not normally performed for the fixed platforms in the GOM.

Several deep water jackets and floating platforms (TLP, SPAR), have reduced the risk of vessel collision by designing/installing protection systems such as platform based radar systems and by the provision of a 500 m radius designated safety zone around the platform with restrictions on entry by unauthorized vessels.

Collisions can occur with in-field vessels (e.g. shuttle tankers, supply vessels, drill rigs/ships, accommodation barges etc.) or with passing traffic such as merchant craft (e.g. ferries, VLCCs etc.). These vessels could be under power or drifting (i.e. environmental forces acting on the vessel) when they collide with the structure. The main causes of powered passing vessel collision tend to be related to watchkeeping failure (e.g. no navigator on the bridge, watchkeeper asleep or radar malfunction). For drifting vessels, the main cause tends to be engine/propulsion unit failure. Such collision incidents have the potential to inflict significant damage to an offshore installation and, for an Floating Production Storage and Offloading (FPSO), puncture of cargo tanks could lead to significant hydrocarbon spillage as well as loss of life, impairment of safety functions, and production loss/delay. In some cases, the damage could lead to fire and explosions, or major structural failure leading to complete loss of the FPSO.

Technologies for collision risk assessment and risk management have advanced within the North Sea, where installations are located away from the shore in proximity to high volumes of passing traffic and where there are also a large number of FPSO facilities whic