Ursa TLP Hull Design, Fabrication and Transportation
Authors: Smith P.L. , Hodges S.B. , Digre K.A. , Sarwono B.A. , Schipper H. 
Published: October 2008

This paper describes the design, fabrication and transportation of the 28,500mt Ursa TLP hull. The process involved a fast track design performed in the USA while fabrication of the hull was underway in Italy. Highlights of major decisions or events will be presented. Unique concerns include:interface with the TLP deck module designers, fabricators and installers,loadout of the hull onto the H-851 transport barge,grillage support for transportation of the hull as a dry tow from Italy to the Gulf of Mexico, later changed to Aruba, andballasting and float-off of the hull from the H-851 in 40m of water.

Introduction

The Ursa TLP hull design, fabrication, loadout and transportation presented many technical and logistical challenges. Because of its immense size compared to previous Gulf of Mexico TLP's, deeper water depth and continually constricting economic pressures, extrapolation from existing designs was infeasible. The only way to clear the ever rising economic hurdles was to "break the mold" and develop new design and fabrication strategies to make step-function gains in schedule and cost. The size of the structure also presented logistical challenges to loadout, transport and off-load a 28,500mt hull in a safe and economic manner. The transport of the largest hull in the Gulf of Mexico on the largest transport barge, HMC's H-851 4, led to a chain of side effects that impacted the design and fabrication of the hull.

The project was approached from the start as an integrated effort between Shell and the various contractors. The step changes achieved were only made possible by leveraging the past experience of both Shell and its contractors. This leverage was not only technical but also relationships and integration between Shell and the contractors.

Building on past experience of both Shell and its contractors, the Ursa hull was designed, fabricated and delivered in 34 months. This was only three months longer than the Ram/Powell TLP hull that weighed half as much. This was achieved by adopting new strategies that included a new deck structure concept and an aggressive design-while-build philosophy.

Project Strategies

The initial project schedule, that showed the hull fabrication being on the critical path by at least four months, proved unacceptable for project economics. Over the course of Shell's TLP hull design experience, the cycle time for design and fabrication has improved substantially with each project. This has been achieved through experience and improvements in design and analysis tools, integration of teams and fabrication improvements. However, in order to cut four months out of the Ursa hull schedule, a step improvement was required.

In the current economic climate of flat or declining oil prices, there are two key drivers for new developments: low life-cycle costs and fast recovery of reserves. For the design of the structure this means, a facility that functions efficiently and with enough flexibility to accommodate changing requirements and as short a schedule as possible to first production. All of these indicators point to a fast-track design, working as many aspects of the project as possible simultaneously to get production on-line faster while reducing capital and operating expenditures. These goals were successfully met on Ursa through cooperation and integration with our contractors and by leveraging the wealth of experience gained in the execution of previous TLP projects: Auger 1, Mars 2 and Ram/Powell. The gains made in schedule alone were instrumental in helping the project clear the economic hurdles.