OTC: Statoil updates subsea installation for Tordis field

Statoil ASA issued a project update at the Offshore Technology Conference in Houston for the world's first full-scale subsea separation system at Tordis field, off Norway.

May 1st, 2007

Nina M. Rach
Drilling Editor

HOUSTON, May 1 -- Statoil ASA issued a project update at the Offshore Technology Conference in Houston for the world's first full-scale subsea separation system at Tordis field, off Norway.

Statoil's Hans Kristiansen told OGJ that Subsea 7 will begin drilling the injector well May 4 using the Bjorland Dolphin rig. Drilling to 1,000 m will take about 40 days, to get to the Utsira formation, Europe's largest salt-water and carbon dioxide storage formation. This will reduce future water discharge into the sea.

The subsea separation station was built by Kongsberg FMC and is scheduled for installation in August. The 1,200-tonne module will be installed in a single lift using the Saipem 7000 heavy-lift vessel. Commissioning is expected to take about 6 weeks, with first production by Oct. 1.

Statoil expects to recover an additional 35 million bbl of oil from Tordis using the new subsea separation system.

Tordis has been producing oil since 1994 through a tieback to Staoil's Gullfaks C platform. Water production has increased to 70-80% over the last few years and sand production to about 500 kg/day. In 2003, Statoil began to plan subsea separation system, boosting, and injection system, in order to prolong production 15-20 years. In 2005, Statoil awarded a $100 million contract for the separation boosting and injection system to FMC Technologies Inc. (OGJ Online, Nov. 10, 2005).

In 2006, CDS Engineering BV and FMC Kongsberg were recognized with an OTC Spotlight award for their Tordis compact subsea separator with integrated solids handling (OGJ, May 8, 2006, p. 25).

FMC's Ann Christin Gjerdseth told OGJ that Statoil installed a small pipeline inline manifold at Tordis in 2006 to reroute the Tordis well stream production to Gullfaks C via the new subsea separation station.

Gjerdseth said the design highlights of the Tordis separator are the internal level detectors for sand, emulsion, water, and oil; and the gas bypass line, which allows the size of the separator to be greatly reduced. The integrated sand management system includes a gravity-based cyclonic device. The sand slurry will be injected downstream of the water injection pump, which was qualified with tungsten carbide impellers, for increased wear resistance.

One of the most significant aspects of the engineering process was moving topside technology to the seafloor, said Gjerdseth. This required a shift to meld the differences between heavily instrumented topside design with the guiding principles of simple, easily replaceable component design for subsea installations, where equipment interaction is limited. FMC worked toward an acceptable level of process control and instrumentation within the short delivery time and limited weather window for installation.

While the current tank design is workable to 1,500 m, the material limit is only about 2,000 m. Ultradeep installations will require inline separation, Gjerdseth said. Future innovations for deepwater projects will include subsea compression facilities and long-distance power transmission.

Contact Nina M. Rach at ninar@ogjonline.com.

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