World's deepest floating production facility nears completion.
One of the most frustrating problems a Gulf of Mexico operator faces is the delay that can be experienced in bringing stranded natural gas fields in ultra deep water on stream.That won't be the case for long, however, given the solution Enterprise Products' Independence Hub provides. This first-of-a-kind offshore facility was recently towed to Mississippi Canyon block 920 and installed in a world record 8,000 feet of water. Later this year, it will begin to facilitate the delivery of approximately 1 Bcf/d of previous stranded natural gas in the ultra deep waters of the eastern Gulf of Mexico.
Owned 80% by affiliates of Enterprise Products Partners L.P. and 20% by Cal Dive International, Inc., Independence Hub is a state-of-the-art 105-foot-deep-draft, semi-submersible platform with a two-level production deck. Anadarko will operate the platform on behalf of Independence Hub (formerly Atwater Valley Producers Group), comprised of Anadarko, Dominion Exploration, Kerr-McGee, Hydro Gulf of Mexico LLC, Devon Energy and Energy Resources Technology.
Fully installed, the Independence Hub will support a total payload (deck, topsides equipment and risers) of approximately 19,000 tons. The hull is designed to carry the loads of one 20-inch diameter export gas line, 16 infield flowlines, and 12 umbilicals supporting production from 10 initial fields.
The platform will process production from the anchor fields Atlas, Atlas NW, San Jacinto, Spiderman, Vortex, Merganser, Jubilee, Mondo NW, Cheyenne, and Q., in addition to future discoveries on surrounding undeveloped blocks.
The anchor producers are Anadarko, Kerr-McGee Oil and Gas, Devon Louisiana Corp., Hydro Gulf of Mexico and Dominion Exploration & Production. The fields will be tied back to the platform through producer-owned subsea flowlines systems located in water depths ranging from 7,800 to 9,000 feet.
Owners say natural gas production from this $2 billion project will represent an increase of approximately 2% of the U.S. supply and increase by 10% natural gas supply from the Gulf.
Design And Construction
Atlantia Offshore Ltd. was contracted by Enterprise for the engineering, procurement, and construction of the ultra deepwater floating production and processing facility and mooring system for the Independence Hub facility in November 2004.
Atlantia's design effort began with an exhaustive analysis of Steel Catenary Riser (SCR) motions and stresses, defining critical areas normally adversely affected by extreme motions. Atlantia then developed the Atlantia DeepDraft Semi rM, a deepwater draft hull design drawing upon the expertise of IHC Caland sister company GustoMSC-Ocean Design (GMOD), an experience designer of marine construction and production semi-submersibles.
Detailed design of the hull, topside primary steel and SCRs was completed in early 2005 and resulted in the design of a 160-foot tall semi-submersible hull with a two-level production deck. The final semi-submersible design was given a payload capacity of 19,300 tons, displacement of 46,160 tons and moored via a 12-leg system.
Construction of the topside and mooring system for Independence Hub was carried out at the Kiewit Offshore Services, Ltd. yard at Ingleside, TX while Jurong Shipyard of Singapore was chosen to construct the 9,000-ton platform hull.
Hull, Topside Mating
On June 19, 2006 the Dockwise's Mighty Servant arrived from Singapore and offloaded the 9,000 ton hull for Independence Hub at the Kiewit Offshore Services yard for final integration with the topsides at quay-side.
On Sept. 20, the topsides were floated onto a barge and floated under the stationary crane at Kiewit's yard where it was lifted off the barge. The hull was then floated under the topsides. Next, the crane was used to carefully lower the topsides onto the hull. The entire sequence took about 10 hours.
Junction Platform
Concurrent with the Independence Hub construction, work was under way on Enterprise's junction platform for installation in the shallow water West Delta Block 68 leasing area.
The deck was later installed on the West Delta 68 platform in the final stage of integration.
At the West Delta 68 site, offshore specialty fabricator Derrick Barge Swing Thompson installed the jacket, piles and deck structure on the seabed in 115 feet of water. The Pace West anchor handling vessel was used to lower the subsea trees on a heave compensated wire system and install them on the wellhead.
The deck structure, built at the Kiewit yard, was later transported and installed by Offshore Specialty Contractors.
Pipeline Construction
Following the first stage of the flowline and SCR installations on the seabed, 134 miles of 24-inch gas export pipeline was manufactured onboard Allseas' vessel Solitaire, welded and then pushed through the stinger assembly and installed in an S-lay method from Mississippi Canyon 920 leasing area to West Delta 68.
Due to the ultra deepwater development, Solitaire, the largest pipelay vessel in the world, had to be modified for this project. This included increasing the ship's buoyancy, installing three new tensioners, a new ANR system and stinger.
During installation of the gas export pipeline the Solitaire added two dual 12-inch and 16-inch inline T-assemblies in 4,500 and 6,500 foot waters, respectively. The installed T-assemblies will provide connections to future development.
Beginning in the Spiderman, Jubilee, Vortex and Cheyenne fields, the Solitaire installed approximately 55 miles of 8- and 10-inch flowline and SCR along with two inline sleds in 8,000 to 9,000 feet of water, making them the deepest flowlines installed to date.
Allseas' vessel Lorelay was used to install an 8-inch infield flowline in the Spiderman, Jubilee, Vortex, Cheyenne and Merganser fields. As part of this work, two additional T-assemblies were installed at the Vortex and Jubilee fields.
Heerema's vessel Balder was pressed into service in the Atlas, Mondo and Spiderman fields to install 24 miles of 8-inch flowline and 7.5 miles of 8-inch infield flowline in the San Jacinto field.
Subsea 7's construction vessel, Toysus Perfurus was mobilized to Aker Kvaerner's Mobile, AL umbilical manufacturing facility to loadout the world's most complex umbilical order.
Six trips from the Mobile facility to Mississippi Canyon Block 920 were required to install the large quantity of umbilical over three months. The umbilicals were laid on the seabed and provide a means to distribute electrical and hydraulic power and chemicals to the subsea wells. The installation and hookup of the subsea umbilical distribution systems by Subsea 7 was carried out over a four-month period. This included installation of the subsea distribution unit and electrical and hydraulic flying leads. An ROV was used to make up all subsea electrical and hydraulic connections.
Following final hookup and installation to the Hub the flowline and export line will undergo an extensive three-month, pre-commissioning process where they will be pigged, hydrotested and dried.
Following pipeline testing and drying, commissioning of the 124-mile, 24-inch diameter Independence Trail export pipeline will occur. Originating in 8,000 feet of water, Independence Trail is the only pipeline through which natural gas can flow from Mississippi Canyon deepwater developments to energy markets onshore via an interconnect with Tennessee Gas Pipeline at Enterprises' new West Delta Block 68 junction platform.
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| Title Annotation: | 2007 Pipeline & Gas Journal's International/Offshore Report; Gulf of Mexico |
|---|---|
| Author: | Tubb, Rita |
| Publication: | Pipeline & Gas Journal |
| Geographic Code: | 0GULF |
| Date: | Apr 1, 2007 |
| Words: | 1158 |
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| Next Article: | Fairings installed during S-Lay pipe installations in ultra deep water. |
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