Post-Mortem Analysis of MODUs in Hurricanes Katrina and Rita

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper OTC 20144, ’Post-Mortem Analysis of MODUs in Hurricanes Katrina and Rita,’ by Malcolm Sharples, Offshore: Risk and Technology Consulting and John Stiff, ABSG Consulting, prepared for the 2009 Offshore Technology Conference, Houston, 4-7 May. The paper has not been peer reviewed. Several hurricanes have passed through the Gulf of Mexico (GOM) resulting in mobile offshore drilling units (MODUs) parting moorings or collapsing, but none have come close to the devastation caused by Hurricanes Katrina and Rita, in August and September 2005. Twenty semisubmersible MODUs suffered significant mooring impairment, and eight jackups were declared total losses (with many more suffering additional settlement and other damage). In the aftermath of these hurricanes, which followed Hurricanes Lili and Ivan, the industry re-examined and upgraded the standards for setting MODUs. Overview of Hurricanes Katrina and Rita In August 2005, Hurricane Katrina moved through the US GOM. Katrina was the second Category-5 hurricane of the 2005 Atlantic season. In September 2005, Hurricane Rita also tracked through the GOM. Hurricane Rita reached Category-5 strength before entering the warm waters of the oil- and gas-exploration regions in the central GOM where it passed over the deeper outer-continental-shelf (OCS) structures as a Category-4 hurricane. Rita weakened to a Category 3 before making landfall along the upper coast of Texas. Sixteen semisubmersible MODUs were in the vicinity of Hurricane Katrina, with two other MODUs stacked, undergoing repairs. Of these MODUs, five suffered complete mooring failure, two had partial failure, and one incurred limited anchor slippage. Most of the semisubmersibles were on the less-severe west side of the storm track. However, Hurricane Rita passed to the south of most of the semisubmersible MODU fleet leading to more MODUs being exposed to severe conditions. Seven semisubmersibles suffered complete mooring failure, four suffered partial failure, and one had limited anchor slippage. The route of Hurricane Rita probably was the worst possible regarding the number of jackups exposed. Many of the jackups were in water depths where the storm was greater than the design extremes, and in many cases the storm was greater than the 100-year extreme for the location. During these hurricanes, there were approximately 90 jackups in the GOM. Of those, 25 jackups were impacted by Katrina and 54 were impacted by Rita. Two were a total loss in Katrina, and six were a total loss in Rita. Of those that survived impact, seven were “surprising survivals” in Hurricane Katrina and sixteen were surprising survivals in Hurricane Rita. Of the jackups damaged, but not destroyed, only three independent-leg jackups and two mat-supported jackups needed to return to the shipyard for repair. Five independent-leg jackups and four mat-supported jackups were repaired on location and returned to work.