Abstract

Hurricane Lili permitted an assessment of the global performance of several deepwater structures under a major environmental event. The objective of this study is therefore to collect and assess information on the performance of the deepwater production facilities that were impacted by Lili.

Lessons learned and recommendations are given in the following major areas: Design Environmental Conditions, TLP Global Performance, Vortex Shedding Effects and Operational Issues. The lessons learned may form the basis for future initiatives to improve the design and operation of deep water floating production units.

1. Introduction

In recent years exploration and production has been steadily moving into deepwater. In the Gulf of Mexico there are currently 30 production units in over 1000ft of water depth, with many more to be added in the future.

Floating production facilities under typical North Sea operating conditions have been investigated in the past with acceptable results. For example, the global performance of the first TLP (Hutton) was concluded1 to be in satisfactory agreement with design predictions. The global performance of the Heidrun TLP was evaluated2 under similar environmental conditions and also concluded to be in agreement with predictions.

Deep water production facilities in the Gulf of Mexico, on the other hand, have experienced operational issues prior to Lili due to aspects such as vortex induced platform motions, the effect of gaps between the air cans and guide supports in spars under wave induced platform motions, vortex shedding effects on tendons and / or risers. These are complex issues that affect different platforms in different ways. An assessment of the behavior of floating production facilities under a major event such as a hurricane may assist in shedding some light on some of these issues.

As far as hurricanes are concerned, the Jolliet TLP was in operation during Hurricane Andrew but it was not in the direct path of that event. Hurricane Lili, on the other hand, allowed an assessment of the global performance of several deepwater structures under a major environmental event.

2. Floating Production Units affected by Lili

Hurricane Lili was the most intense hurricane of the 2002 season. As it moved across the Caribbean, Lili fluctuated in intensity and was a Category 1 hurricane near western Cuba on October 1st, 2002. Between Cuba and Louisiana, Lili intensified to 145 knots wind speed (Category 4 Hurricane) on October 2nd, 2002 and maintained intensity into October 3rd, 2002. It suddenly lost intensity and was a much weaker hurricane by landfall.

Lili was a Category 4 hurricane while over the north-central Gulf of Mexico and during the early hours of October 3rd, 2002 it passed through the Green Canyon and Eugene Island areas, impacting several Tension Leg Platforms (TLPs) and a spar, Figure 1 and Table 1.

Figure 1 -Floating Production Units near Lili's Track (Available in full paper)

Table 1 - Floating Production Units near Lili's Track(Available in full paper)

A hindcast study permitted the maximum environmental conditions such units were exposed to be estimated and the results are given in Table 2.

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