Jameel, Mohammed (Department of Civil Engineering, University of Malaya) | Saiful Islam, A.B.M. (Department of Civil Engineering, University of Malaya) | Jumaat, Mohd Zamin (Department of Civil Engineering, University of Malaya) | Ahmad, Suhail (Department of Applied Mechanics, Indian Institute of Technology Delhi (IIT Delhi))
A floating platform for arctic regions is required to break ice and withstand high ice loads, be disconnected and towed away in the event of approaching icebergs, leaving the mooring lines and risers in-place, support large topsides and provide large quantities of utility storage. Additionally the platform should provide low motion response to storm and ice loads to maximize the operational uptime and enable the use of current state-of-the-art riser systems.
This paper presents the details of a Spar platform that has been configured to satisfy all requirements for Arctic operation. The paper describes a number of key features that are specifically designed to reduce ice loads on the hull and to allow ice floes to break around the hull without damaging the hull, topsides, mooring or risers, while maintaining the characteristic low motion response to storm environments. The paper also describes the system for disconnecting and reconnecting the moorings and risers in response to approaching large icebergs.
This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper OTC 20885, "Perdido Development Project - Spar and Moorings," by Curtis Lohr and Keith Smith, Shell International Exploration and Production, prepared for the 2010 Offshore Technology Conference, Houston, 3-6 May. The paper has not been peer reviewed.
A Spar was selected for the Perdido Development during system selection in 2005 to provide a stable platform for direct vertical access drilling and producing operations for the world's deepest drilling and production platform in nearly 8000 feet of water. A combination polyester / chain mooring system was selected to place less vertical load on the floating structure (compared to a steel mooring system), which results in less payload on the structure and a lower overall cost solution for the project's host platform.
The transportation and installation of the Perdido Spar and moorings was completed during 2008. A number of records were set during the installation campaign including the world's deepest Spar installed in 7817 feet of water and the world's deepest permanent mooring pile in 8631 feet of water.
Challenges of interest to the offshore industry that contributed to the uniqueness of the Perdido Spar and moorings were:
• Impacts of Topsides single lift on the Spar design and weight management
• Safety management given a project goal of zero recordable injuries
• Ultra deep water location with increased environmental requirements and significant seafloor hazards
• Polyester permanent mooring system
• Spar fixed ballast installation accuracy
• Spar installation during hurricane season
This paper will provide a broad overview of various aspects of the Perdido Development Spar and mooring system design, fabrication, transportation and installation while highlighting the main challenges encountered and lessons learned for future projects.
During the last seven years Heerema Marine Contractors (HMC) has installed more than half of all Spars in the deep waters of the Gulf of Mexico. The dual crane deepwater construction vessels have proven repeatedly that a complete Spar installation, from piles to hull, topsides and SCR (Steel Catenary Riser), can be performed very efficiently with a single vessel.
Since the first Spar was installed, significant challenges have been overcome throughout every phase of the Spar installation. Spar anchor piles for example have included installation of both driven piles in water depths of up to 4,900 ft, and of suction piles in 8,600 ft of water. Another good example is a recent industry first, where the VIV strakes on the belly side of a Spar were installed offshore. This offshore installation eliminates the need to compromise in the design of these VIV strakes, which will be beneficial for the Spar during the rest of its operational life.
The advantages of using installation vessels with large deck space and with dual cranes with a high lifting capacity, is demonstrated in almost all phases of the Spar installation. A large deck area with dual cranes allows for easy handling and upending of items such as piles and Aircans. At the same time it is also possible to store several mooring lines on the deck at once, allowing for flexibility in the order in which these lines are installed. An additional advantage of the Deepwater Construction Vessel (DCV) Balder is that it has installed both Spiral Strand Wire and Polyester mooring lines with the 10.6 m diameter Mooring Line Deployment (MLD) winch. The Semi Submersible Crane Vessel (SSCV) Thialf has recently been outfitted with a similar capability.
HMC is best known for its heavy lifting capacity, which is reflected by the installation of Spar topsides with modules of up to 8,695 st. The large weight allows significant savings in cost by outfitting most topsides components onshore at a yard.
A specific example of tools used in order to obtain flexibility is given by means of the in-house developed Mooring Line Hook-up software. This software allows greater insight in the various forces acting on the Spar and the installation vessel. Software such as this allows making offshore decisions for the best route forward during the installation of mooring lines, while reducing overall risks and downtime. It is shown that especially during the installation of polyester mooring lines, where the forces are less well known in advance due to fabrication tolerances, an adjustable procedure has its advantages.
In 2008 HMC introduced the Incident and Injury Free (IIF) program. This program aims to change the mindset from one of "accidents happen?? to one where working incident and injury free all the time is achievable for everybody.
In conclusion this paper shows that all three of HMC's installation vessels have proven that they are capable of deepwater Spar installation. HMC has the advantage of having two vessels with similar deepwater capability, providing considerable savings on mobilization, mode change and weather downtime and allowing greater schedule flexibility.
The Arctic is the next frontier for oil and gas production, and it will offer new challenges for engineers who must design safe and efficient systems to operate under new environments. Some designs will be based on existing ones modified for these new conditions. In this paper, two floater designs, a Spar and Single Column Floater (SCF), are evaluated for deployment in an arctic environment. The floaters are assumed to support identical topsides and riser payloads and to be subjected to the same environments composed of level ice sheets and ice ridges, wind, waves and currents. Hull steel weights and mooring systems are similar for both designs. The comparison is based on general arrangements and global performance comparing motions responses and moorings loads. Results show that the motion global performance of the SCF is marginally better than the Spar. The ice breaking cone, used on both designs, shows unacceptable heave response on the hulls, requiring them to change drafts depending on whether the environments present ice cover or open-water conditions.
Ward, G. (Offshore Technology Research Center, Texas A&M University ) | Hansen, Vigleik L. (Det Norske Veritas) | Kim, Moo-Hyun (Offshore Technology Research Center, Texas A&M University ) | Wang, Lihua (Det Norske Veritas)