Snorre Project Execution
Authors: Solheim B.J. 
Published: December 2007

The Snorre field is the first truly deepwater North Sea development. It contains the largest tension-leg platform (TLP) installed to date and a large remote subsea production system. The platform went on production in Aug. 1992.Execution of large projects that use a lot of new technology provides special challenges. This article describes the project execution with a special focus on the extensive marine operations involving about 100 different activities.

Introduction

The Snorre field is in the northern part of the North Sea, about 150 km west of Floro on the Norwegian west coast. Saga Petro leum A/S is the field operator. Other owners are Statoil, Esso Norway, Deminex Norway, Idemitsu Norway, Norsk Hydro, Elf Norway, Amerada Hess Norway, and Enterprise Oil Norway.

The field will be developed in two phases. Phase 1 was installation of a TLP and a sub sea production system (SPS) in 310- to 335-m-deep water. Phase 2 is further subsea development of the northern area, with about 20 wells tied back to the Snorre TLP. Both Phase 1 installations are the largest of their kind in the world today. About 40 wells will be drilled from the TLP, 10 wells will be drilled from the SPS, and 10 additional wells can be drilled if required. Oil and gas from both installations are partially processed on the TLP and shipped by pipelines to the Statfjord A platform, 28 km away, for final processing and offshore tanker loading. Recoverable reserves are 141.5×106 std m3 oil, 8.9×109std m3 gas, and 4.5×106 Mg natural gas liquids.

The TLP well template was installed in the summer of 1990, and six production wells were predrilled before TLP installation in May 1992.Production began on August 3, 1992, 1.5 months earlier than planned. Production costs were about $200 million under budget. Total project cost was about $3billion, and about 10,000 personnel were employed during the peak production period. Current production is about 27×103 m3/d, with peak rate estimated at 30×103 m3/d.

The SPS was installed at a 335-m depth in May 1992. After extensive commissioning and testing, production started in April 1993.

Preproject Phase

One of the strategies implemented by the Snorre management was to conduct a thorough preproject exploration, planning, and evaluation phase. The major challenges were the more than 300-m water depth, a large and complex reservoir, and the dramatic oil price drop that occurred in the mid-1980's.

The Snorre team spent 3.5 years and $150 million to explore and evaluate the field before project start. Exploration was carried out at the same time as reservoir definition, development planning/evaluation, conceptual engineering, and cost/schedule development. There was no preengineering period before the start of detailed engineering.

Factors that contributed to project success include the following.The preproject evaluation team was organized as a team with the same organizational structure and procedures. This provided a core group of about100 people at the project start familiar with work procedures and committed to the concept.All relevant skills and disciplines were included under the same management (exploration, reservoir, planning, and engineering).Approximately 14 structural concepts and a variety of options and business conditions were thoroughly evaluated. Five cycles of conceptual design were carried out in the selected concept.A solid industrial base was prepared through fabrication studies, tether-concept design and development, engineering and procurement studies, and materials-testing programs.

TLP Construction, Hookup, and Commissioning

TLP construction was bid under favorable market conditions. This led to an initial beneficial cost picture for the project but put the site teams underpressure to contain cost growth owing to variations. Quality and scheduling were managed well. Construction interfaces were well managed, and strong emphasis was placed on a number of dimensional control activities to verify that nodules and structures were well inside construction tolerances before installation. Extensive punch-listing of interfaces with the Snorre project team and contractors led to reasonable levels of undetected carry-over work, which has been a serious problem on previous projects that resulted inextensive reworking at a late stage. The main lessons learned included the following.There were few major, but many minor, design changes. Considering all factors, this was probably acceptable; however, more emphasis on design quality is warranted.Mechanical completion of deck systems and areas was not carried out in the proper sequence for commissioning owing to late or incomplete fabrication drawings. This problem had been anticipated.

Hookup and commissioning were carried out at an inshore location, adjacent to the deck-fabrication site. Commissioning was carried out by the project team with assistance from the deck-fabrication contractor and the platform control system vender. Several factors contributed to success. The integrated-deck concept allowed a high degree of completion inshore, all possible major systems were tested, and management was able to focus the construction and commissioning on high-priority areas, such as early completion of all safety systems, completion of the drilling system, the tether systems, and the subsea interface.

Tethers and Risers

Manufacturing of tethers and risers was a high-technology area that required special attention.

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