Independent takes unconventional approach to hub-and-spoke solution
Gomez achieves first production through converted MODU
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David Paganie, Senior Editor
Given the industry’s favorable pricing environment, operators are taking unconventional approaches to fasttrack production.
Take ATP Oil & Gas’ latest deepwater development. The independent achieved first production on March 9 through a converted semisubmersible production facility on the Gomez field in Mississippi Canyon block 711.
This is the first unit of this type installed in Gulf of Mexico waters since 1995 when Enserch Exploration produced oil through a converted semi on the Cooper field in Garden Banks block 388. TheEnserch 388, or Enserch Garden Banks, was later decommissioned in 1999.
Various deepwater production facilities have been installed in the GoM since the 1970s, but only a handful of times has an operator opted to employ a semisubmersible-type unit. TheGomez platform joins two existing newbuild semisubmersible production systems, Thunder Horse and Na Kika. An additional three newbuild semis are planned for installation over the next two years: Independence Hub, Atlantis, and Blind Faith.
Selection criteria
Through conceptual engineering work and other design studies, ATP determined it feasible to exploit Gomez’s marginal reserves through a semisubmersible production facility, converted from an existing MODU. “We believed the schedule of a converted semi would be much faster compared to a newbuild TLP, spar, or semi, and we wanted to achieve first production quickly”, says Leland Tate, ATP’s COO.
The operator agreed to acquire theRowan Midland MODU from a subsidiary of Rowan Companies in October 2005 for $60 million to serve as the floating production hub for the area in and around the Gomez field in MC 711. Prior to then, ATP held the semi under a lease-term agreement. “We acquired the facility about half-way through the process leading up to first production primarily due to positive flow results from the first two wells,” says Tate.
“The semi will remain onsite until we are finished producing through it, and then we plan to move it to a new field,” he says. “It is not unreasonable to expect that Gomez will produce through the semi for five to ten years.”
T. Paul Bulmahn, ATP’s chairman and president, says that the acquisition of the semi increases the company’s short-term and long-term operating flexibility.
The company plans to pay off the balance of the semi’s lease on Jan. 31, 2007, after which it will assume 100% ownership. Total capital expenditures related to acquisition, conversion, and other associated expenses amounted to around $100 million.
Pegasus International, under subcontract to project manager Bluewater Industries, on behalf of ATP played an integral role in selecting the Gomez field development plan. The engineering company performed FEED and detailed design studies for the project’s subsea production system, pipelines, and the converted semi’s topside process modules. It also provided project management support, inspection, and construction coordination.
Fasttrack conversion
TheRowan Midland MODU arrived at Signal International’s dry-dock in Port Arthur, Texas on Sept. 18, 2005 for conversion into a production platform. Critical path items performed by Signal at the dock, which lead to a successful delivery, included fabrication of components for the unit’s upper and lower guides, integration of constructed modules while the vessel was docked, and alignment and integration of the multiple pull-tube assemblies with the guides.
Following the four-month stint at the dry-dock with over 100,000 man-hours logged, the semi was undocked and moved to Signal’s Texas South Yard in Sabine Pass, Texas for final outfitting.
Here the MODU’s derrick and associated drilling equipment were removed, leaving behind limited well intervention capabilities. The semi’s leftover drilling capacity can be used to perform minimal thru-tubing work for re-entering wells situated beneath the floater, but it cannot spud new wells.
After a majority of the drilling equipment was removed, the semi’s production modules were installed. Omega Services of New Iberia, Louisiana fabricated and supplied the process modules, which were then fitted atop the semi’s upper deck with Horizon Offshore’s derrick bargePacific Horizon. Major installed process equipment includes HP, LP, IP and test separators, gas turbine compression, glycol compression, electrostatic heater treater, LACT, gas sales metering, and gas turbine generators.
The floater was then transferred to Signal’s yard in Pascagoula, Mississippi for stability testing. The overall duration of the program for converting the drilling rig into a production facility took five months. Tate says the period of conversion work would have been reduced by one month without delays caused by hurricanes Katrina and Rita.
In early January, the converted semi was towed out and took up station in approximately 3,000 ft of water on MC 711.
Mooring alternative
TheGomez semisubmersible floating production platform is permanently moored by a 12-point taut-leg mooring system with polyester rope, fixed to the seabed via suction embedded plate anchors (SEPLAs). The SEPLA is a patented InterMoor product. According to the supplier, this is the first time a floating production unit is using SEPLA anchors in the GoM.
The mooring system components include (from semi to seabed) about 700 ft of 3.25-in. wire on 8 legs, or 3-in. chain on 4 legs, approximately 4,340 ft of 6.5-in. torque-matched polyester rope, 600 ft of 3-in. chain, subsea connectors, 200 ft of 3-in. chain, and the SEPLA anchors.
According to InterMoor, SEPLAs are significantly more cost-effective than the more traditional suction embedded anchors. This particular application was also among the world’s first to use polyester rope, which provides lower cost and better performance (lower tensions and semi offset) than conventional steel catenary systems, adds the company.
The mooring system has a design life of 10 years and has enough capacity to withstand 200-year storm conditions. Originally, the mooring was designed for 100-yr hurricane conditions based on API RP 2SK factors of safety. This design was performed with the drilling derrick still on theMidland. After the MODU’s derrick and associated drilling equipment was removed, the analysis was redone. The semi’s stability and station keeping significantly improved and the environmental forces due to wind loading were reduced after removal of the associated drilling facilities.
The individual components of the mooring system also passed an ABS design review, including break tests. Each of the mooring legs was proof loaded in the field to at least 80% of the maximum intact 100-year hurricane load.
InterMoor managed installation of the mooring system as well. It was conducted in three phases. The SEPLA installation was performed from Saipem’s construction vesselNormand Cutter. Setting of the polyester rope followed with assistance from Maersk’s anchor handling tug supply vessel, Maersk Assister, and SEACOR Marine’s anchor handling tug and supply vessel, Seacor Vision. The final phase included hook-up of the semi to the moorings.
Subsea production
At print, two subsea wells (No. 4ST1 & No. 6) drilled on the southern portion of MC 711 were flowing to the moored semi. Diamond Offshore’s semisubmersible drilling rig,Ocean Voyager, re-entered and completed the two wells.
The initial two subsea wells, under the first phase of Gomez, are tied back to the semi for processing. Dril-Quip supplied the subsea trees, wellheads, and controls. TheSeaway Defender and Midnight Express performed installation of the subsea production components, jumpers connected to the trees, and infield flowines. The export risers fixed to the floater, comprising one 6-in. oil line and one 8-in. gas line, were supplied by NKT Flexibles. The three, 4-in. flexible flowlines were supplied by Wellstream International.
Power for the subsea wells is supplied to the semi through dual 1.4-mi, 4-in. dynamic hydraulic umbilicals with lazy wave touchdown and integrated 2-in. gas lift service lines, delivered by Cabett Subsea and installed by theMidnight Express. Cabett supplied rigid gas lift jumpers and hydraulic flying leads for the subsea trees and UTAs as well. The contractor delivered all subsea UTAs and associated interface equipment through an alliance with Unitech USA.
Oil production fromGomez is exported through 27 mi of 8-in. pipeline to a 12-in. subsea tie-in point in Grand Isle block 115, and gas sales is exported through 27 mi of 10-in. pipeline to a 20-in. subsea tie-in point in GI 115 as well. The export pipelines were installed by Helix Energy Solutions’ (prev. Cal Dive) pipelay vessel Intrepid.
TheGomez floating production unit is equipped with capacity to handle 25,000 b/d of oil, 15,000 b/d of water, 50 MMcf/d of natural gas, and is fitted with accommodations for 98 people. All produced water will be disposed of according to regulation, and gas will be sold through the Discovery Pipeline System. The production semi is also designed to accommodate up to three direct subsea wells, but is expandable to handle 6 to 10. Installation of a subsea manifold will be required at the time of facility expansion to accommodate increased flow from additional wells.
The operator has contracted Diamond’s semisubmersible drilling rigOcean Quest to exploit the northern segment of the project area, comprising adjacent blocks MC 667 and MC 668, which ATP acquired in 2005. This work scope falls under the second phase of the Gomez project, which is scheduled during 2006-2007. The operator is committed to drill at least four wells on Gomez over the next two years.
ATP owns a 100% working interest in the Gomez development project. The MC 711 block, acquired by the operator in 3Q 2003, contains proved and probable reserves of approximately 140 bcfe. The field’s initial discovery well was drilled in 1997 by a company subsequently acquired by Anadarko. The field’s commercial potential was later confirmed in 2000 with the drilling of well No. 4 and well No. 4 ST1.