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 ft. 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. 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.