Stolt Offshore in Houston has successfully completed a deepwater subsea to subsea installation, including one flowline and one umbilical, for Shell’s single well Einset project in the Gulf of Mexico, reports Bjorn Koi, Stolt’s project manager.
“Subsea to subsea installations are ‘rare’ in the industry but may become more prevalent as we move into deeper waters. To date, most subsea tie-backs have been supported by host platforms in shallower water.
“In the case of Einset, we tied back a new deepwater well
to existing subsea infrastructure, also located in deepwater. This achievement demonstrates how the industry is applying proven technology while effectively utilizing deepwater construction vessels, such as Stolt’s ‘Seaway Falcon’,” said Koi.
He added that the “Seaway Falcon” multipurpose vessel achieved its deepest pipelay to date, with the Shell Einset well located in 3,463 feet of water on Viosca Knoll Block 872.
The Stolt crew completed the umbilical and flowline installation project in a single mobilization, using a J-lay installation method. Incorporating the use Stolt’s SERIMER DASA Saturnax automatic welding system on board the “Seaway Falcon,” the crew assured the quality of the welds, without any repairs required. From Einset, the “Falcon” installed a six-inch diameter flowline 5.3 miles to lay down at the SE Tahoe 1 satellite well in 1,800 feet of water.
The “Falcon” also installed 7.4 miles of Shell’s “EH” umbilical from Einset to Shell’s Tahoe UTS facility 1,500 feet of water. Stolt installed the umbilical from a reel on deck through the “Falcon’s” flexible lay system (FLS) situated above the vessel’s moonpool. The SE Tahoe 1 well and Tahoe UTS facility tie back to an existing Shell-operated platform on Main Pass Block 252 in 276 feet of water.
The Einset project, advises Koi, presented several technical challenges. Stolt began the fast-track project in early August 2001, mobilized its vessels and equipment by mid-October and successfully completed the project by Oct. 31, as scheduled.
The joint efforts of the entire project team, including Shell, Stolt and the subcontractors, met the fast-track challenge, completing the Einset project safely and without incident, says Andrew Culwell, Stolt’s marine construction manager.
“As with all our projects, we worked proactively with the full team to plan our work and to ensure the safety of all project participants, equipment and the environment,” said Culwell.
The project scope included the setting of two long base line (LBL) arrays—a collection of acoustic beacons or transponders—to ensure the accurate installation of two Shell-supplied pipeline end manifolds (PLEMs) at each end of the six-inch flowline; i.e., one at the Einset well and one at the SE Tahoe 1 well. The two pipeline jumpers, installed by others, connected the PLEMs to the wells.
Stolt’s “Seaway Rover” ROV (remotely operated vehicle) support and survey vessel completed the LBL arrays, installing six transponders at Einset and eight transponders at SE Tahoe 1 in advance of the flowline installation work.
“The accuracy rate in using the LBL array is very high. We hit our target boxes for installing the PLEMs with excellent precision due to the good work of the ‘Seaway Falcon,’” said Koi.
The PLEMs themselves represented a challenge as well, says Koi, explaining that Stolt designed and fabricated a purpose-built PLEM handling frame to accommodate their size and facilitate installation. Each PLEM was approximately 25 feet tall, with the PLEM installed at Einset weighing 24 metric tons and the PLEM at for the SE Tahoe location weighing 18 metric tons.
Stolt installed the PLEM handling frame on the “Seaway Falcon’s” port side to facilitate manual welding the PLEMS to each end of the flowline, which Stolt lifted from the seabed floor to secure the pipe in the frame.
Stolt completed the welds on the deck of the “Seaway Falcon” and then lowered the flowline and each PLEM to the target locations at each well site for final lay down. The crew of the “Seaway Falcon” used the vessel’s two permanently installed work-class ROVs to successfully complete the flowline and PLEM installations.
For the umbilical installation, Stolt’s work included four flying leads—one steel flying lead at the Einset well and three thermoplastic/electrical flying leads at Shell’s Tahoe UTS facility—to bring power and controls to the new well. Stolt’s “Seaway Rover” provided support, installing a temporary parking frame at Einset to connect the flying lead to the well tree.
Other project support provided by the “Seaway Rover” included the installation of two mud mats for the umbilical termination assemblies at Einset and the installation of 10 concrete mattresses over an existing 16-inch diameter pipeline for its protection. The “Seaway Falcon” installed the six-inch diameter flowline over the existing pipeline. A separate contractor completed hydrotesting of the new flowline.