Abstract

The paper describes the analyses and procedures used to recover a jack-up which had been hit by Hurricane Rita and though still standing took on a tilt of three degrees and suffered some leg damage. Initial recovery attempts resulted in further leg damage at which stage it was decided to apply temporary leg strengthening and undertake a more detailed evaluation and analysis of the best methods of recovering the unit. The strength of the soils was found to be providing restraint which helped to support the tilted configuration but was also having the effect of resisting the leveling of the unit and thereby causing further leg damage. The analysis identified the need for a hold-back force during the recovery procedure to prevent further bracing damage in the legs and avoid a complete collapse mechanism developing. A suitable barge pull-back system was developed and in December the operation to recover the unit took place successfully.

Introduction

In September 2005 Hurricane Rita moved into the Gulf of Mexico and resulted in considerable damage to oilfield installations in the area. At the time the three-leg jack-up platform GSF High Island II (GSF HI-II) was located in South Marsh Island Block 90 beside a tripod structure wellhead. The water depth was 163 ft (49.7 m) and the jack-up had a heading of 328 degrees. The air gap between the still water level and the keel was 72 ft (21.9 m) and the spudcan penetrations were 17 ft (5.2 m) on the two aft legs and 15 ft (4.6 m) at the bow. The elevated hull weight at the time was 11,200 kips (5,081 tonne).

Prior to arrival of the storm the rig was made secure and de-manned. The eye of the storm passed to the south and west of the platform (see Fig 1). Hind casting analysis has shown that the 30-minute average wind speeds seen at Block 90 were about 85 knots (44 m/s) and the significant wave height reached 37 ft (11.3 m) with a peak period of about 14.5 seconds. Note that in Fig 1 the numbers in the white boxes are 1-minute average; the contours are 30-minute average.

Fig 1 : 30-minute average wind speed contours for Rita

The jack-up was re-manned after the hurricane on 29th September. At that time the unit was noted to be down by the bow by 3 degrees and down to starboard by 0.4 degrees. A representative view of the condition at that time is seen in Fig 2. Upon inspection it was noted then that there was some cracking in the leg brace welds and some superficial damage but otherwise the jack-up was in good condition. The jacking equipment was all functional.

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