Tyrihans, Norwegian Sea, Norway

Tyrihans is located on the Haltenbank in the Norwegian Sea, 35km southeast of the Kristin field in roughly 285m of water.

The discovery comprises two structures - Tyrihans North and Tyrihans South. Part of the Tyrihans South field extends into production licence 091, while Tyrihans North lies exclusively within production licence 073.

Drilling in the Tyrihans field began in April 2008 and it was not until 8 July 2009 that the production had commenced. The production at the field is expected to last until 2029.

Recoverable reserves are put at roughly 186 million barrels of oil and condensate, and 41.5 million cubic metres of rich gas. Statoil has a 58.84% interest. Its partners are Total E&P Norge with 23.18%, Eni Norge 6.23% and Mobil Development Norway 11.75%.

Gas and liquid export

In July 2005, Statoil submitted a PDO (Plan for Development and Operation) for Tyrihans and began procurement. A 43km pipeline carries the wellstream to the platform for separation.

The rich gas from both fields is then exported via the Åsgard Transport system which runs to Kårstø, north of Stavanger. There, the gas is processed before onward transmission to European customers.

Meanwhile, the liquids production - condensate and crude - is combined with Kristin output after stabilisation and piped to the Åsgard C storage ship for export by shuttle tanker.

Discovery and appraisal

In 1984, the Tyrihans Nor discovery well 6407/1-3 found hydrocarbons at 3,600m in the middle Jurassic sandstones. It was drilled by the Dyvi Delta. A gas cap extended to 3,687.5m followed by an oil zone down to 3,709m. The Dyvi Delta had previously drilled the Tyrihans Sor wildcat well 6407/1-2.

The Tyrihans Nor well was followed by the 6407/1-4 appraisal, drilled by the Byford Dolphin in 1996 to 3,805m, while in 2002 a Tyrihans Sor appraisal was drilled by the Stena Don.

Development

Tyrihans has been developed with a total of 12 wells, some multilateral, breaking down to nine for production, two for gas injection and one for the injection of unprocessed seawater. The wells will also include the use of smart well technology for improved recovery from subsea-completed fields.

All the wells are connected to five subsea templates. Statoil had entered a three-year, NOK2bn agreement to use the Transocean Arctic semisubmersible for drilling and completion.

Subsea pumps will be used for injection of seawater, while gas will also be injected from the Åsgard field. Statoil awarded FMC Kongsberg a $225.4m contract for the subsea systems. This covers assistance and maintenance of the facility during installation and operation

Subsea system

The seabed installations on the field were carried out in 2007. All the 12 wells are held with the help of four production frames, which are in turn connected to the Kristin pipeline. Gas supply for gas injection and gas lift in the production wells is compensated from Aasgard B pipeline.

The planning of gas injection has been done to last until 2015. Injection of sea water for pressure support will commence in 2010 and is planned to last till 2016. The injection will be done through a subsea facility which has already been installed.

Pipelines

An electrically heated pipeline links Tyrihans with the Kristin platform. Tyrihans connects to Kristin through a 43km, 16in pipeline whereas Tyrihans connects to Aasgard B through a 10in pipeline.

Statoil let a NOK300m contract to Butting of Germany for the December 2006 delivery of steel pipe for the pipeline, which was successfully delivered in December 2006.

The pipeline was laid in 2007. Ramboell Denmark SA conducted the engineering for the pipelines and their routes.

The pipeline for the wellstream is made of special steel. It consists of an outer carbon pipe and an inner stainless steel pipe. This is the first time that Statoil has installed such a pipeline. The operator had awarded Stolt Offshore (Acergy) the work to lay two pipelines from Tyrihans to Kristin. The contract is worth over NOK550m.

Production

The Aasgard B platform required modification, as will Kristin, although some modifications were made while the platform was under construction. A 250t processing module was built and installed on the platform in 2008.

Plateau production is expected to be about 96,000 boepd by 2016-17, while Statoil's share is expected to be 56,000 boepd.