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A Look at the Aasta Hansteen Norwegian Deepwater Spar FPSO

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The complete paper describes the overall project execution of the Aasta Hansteen field development on the Norwegian Continental Shelf (NCS) north of the Arctic Circle. It is the deepest field yet developed on the NCS in 1300 m of water. In a harsh environment, with no other offshore installations in the area, the field is being developed with a spar floating, production, storage, and offloading (FPSO) structure using steel catenary risers and polyester mooring lines.

Business Case

The field is 300 km off the coast of northern Norway and 140 km from the nearest offshore installation. The field was discovered in 1997, with investment decision taken in December 2012 and production begun in December 2018. Total investment in facilities and infrastructure (including pipeline and modifications at Nyhamna) is approximately $7 billion. Equinor operates the field on behalf of its partners, Wintershall (24%), OMV (15%), and ConocoPhillips (10%).

The field’s rich gas is exported through a 482-km-long, 36-in. pipeline to an onshore processing plant at Nyhamna for further processing to sales gas. From there, the gas is exported to the European market. Stabilized condensate is stored in the spar FPSO and offloaded to shuttle tankers.

The development of the field with the platform facilities and the Polarled pipeline was a strategic decision to open a new gas region in the Norwegian Sea and connect it to Europe by the NCS gas infrastructure. The development solution will serve as a gas hub enabling tie-in of future production from discoveries and prospects in the area. The objective of the Aasta Hansteen development is to maximize the recovery of the Aasta Hansteen reserves and to achieve maximum value creation in the value chain.

Estimated recoverable reserves are 51 billion scm rich gas and 0.6 million scm condensate. The reserves consist of three separate discoveries—Luva, Haklang, and Snefrid Sør—all in the Nise formation and within the same production license.

The development of Aasta Hansteen has been executed as a parallel development of the Polarled pipeline project to establish a new gas transport pipeline from Aasta Hansteen to Nyhamna. The pipeline has several tie-in points from Aasta Hansteen to the Nyhamna gas-processing plant. Snefrid Nord, the first subsea tieback development, is already being developed. The complete paper provides a brief description of the Polarled project.

Development Concept and Technology Selection

Important parameters for selection of field-development concepts at Aasta Hansteen were deep water, harsh environment, distance from shore (300 km), and need for condensate storage and offloading. Initially several field development concepts in a wide range were studied, including the following:

  • Subsea tieback with multiphase flow to shore (similar to the Ormen Lange development in the Norwegian Sea)
  • Subsea tieback with multiphase flow to a shallow-water floater with condensate storage, offloading to shuttle tankers, and export of rich gas to Nyhamna
  • Subsea tieback to an existing platform on Halten (gas export in pipeline)

Economy and robustness against change in reservoir conditions drove the decision to proceed with a freestanding deepwater floater. The deepwater floater was also more attractive for future business opportunities. A wide range of standalone floaters at the field was then studied further. These included semisubmersibles, tension leg platforms, a circulator FPSO, a ship-shaped FPSO, and classic and truss spars. The selected floater solution is an integrated combination of hull, mooring, and riser considered as one system. The final candidates were the two spar concepts, both with condensate storage and carrying steel catenary risers.

The final development concept uses a floating truss spar FPSO tied to a subsea production system (Fig. 1). The platform is designed for normally manned operation with 34 personnel on board. Maintenance is to be performed on a campaign basis. Because of the harsh environment and condensate storage, volume in the spar hull was used for selected equipment. Condensate-storage, freshwater-storage, seawater-cooling, ballast and bilge, and other relevant support systems are located in the hull, which is intermittently manned. Thus the spar is unusually complex, consisting of pump rooms, equipment rooms, ventilation, staircases and escape routes, elevator, lighting, and other systems (Fig. 2).

Fig. 1—Aasta Hansteen facilities.
Fig. 2—Aasta Hansteen spar.

 

The complete paper discusses the project’s technology qualification programs. It also presents a detailed discussion of the topsides, subsea and gas-processing facilities and processes, and subsurface operations.

Project Execution

During project execution, project teams were located in the US, Europe, and Asia. To comply with the Norwegian PSA/NORSOK regulation for operators’ followup of the contractors’ work and to reduce the challenges with interfaces between the subprojects, the operator established multidisciplinary followup teams in the offices of all major contractors with a coordinating home office located in Norway. Work through the different timezones created special needs for coordination meetings between all teams. Project management followed different phases of the project and was located at the engineering contractor during the engineering phase, at the fabrication yard during construction, and at the mating and completion yard in the last phase before the tow to field.

The extraordinary complexity of the project, especially with regard to the spar, was recognized early by both contractors and the operator. This affected the execution for both engineering and construction. The complete paper discusses the overall contracting strategy, contractor selection for various aspects of the development, and overall construction work and marine-operations sequences.

Conclusions

  • The Aasta Hansteen project has achieved several noteworthy world-first milestones, detailed in the complete paper.
  • The project demonstrated the operator’s capability to execute successfully a large deepwater field-development project for a harsh environment in conjunction with contributions from partners, major contractors, and suppliers.
  • Gas production at Aasta Hansteen began on 16 December 2018. All wells have thus far performed as expected.
  • After resolving some startup challenges, the processing and utility systems have performed at a level that lives up to production-efficiency expectations.
  • The first tieback development, Snefrid Nord, was in the execution phase at the time the paper was written, with production startup scheduled for Q4 2019. The development is based on Aasta Hansteen technical solutions and using the same suppliers, and the well was drilled as a part of the seven-well campaign on Aasta Hansteen. This execution strategy secured a fast-track, low-cost project, providing high value for the owners.
This article, written by JPT Technology Editor Judy Feder, contains highlights of paper OTC 29222, “Aasta Hansteen Spar FPSO—A Pioneer in Norwegian Deepwater,” by Torolf Christensen, Stig Arne Witsøe, and Helge Hagen, Equinor, et al., prepared for the 2019 Offshore Technology Conference, Houston, 6–9 May. The paper has not been peer reviewed. Copyright 2019 Offshore Technology Conference. Reproduced by permission.

A Look at the Aasta Hansteen Norwegian Deepwater Spar FPSO

01 May 2020

Volume: 72 | Issue: 5

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