The costs of developing deepwater Gulf of Mexico discoveries into producing properties is driving the rise in the use of hub-and-spoke field arrangements. The use of the technique has proven sufficiently successful leading efforts to move the same development scheme into shallower waters.
US Department of the Interior Minerals Management Service statistics through the first half of 2006 account for 54 existing facilities either acting as or capable of acting as a hub. Looking ahead, the MMS finds 10 more deepwater locations scheduled to get facilities that could be used as a hub upon installation.
The type of facility used tends to change with the water depth of the field. In the shallow waters, almost all the installations are either TLPs or fixed platforms. In the deeper waters, the installations are divided among TLPs, spars, and an “other” category collecting compliant towers, semisubmersibles, and FPSs. Looking further ahead, the potential locations identified are expected to see spars or “other.” The “other” in this case is likely to consist of semisubmersibles and FPSOs. Petrobras recently received permission to bring in the first GoM FPSO.
One company is working on the concept of using a hub-and-spoke system to develop multiple fields and also to use movable facilities for more economically marginal fields. Helix Energy Solutions’ Marginal Prospect Development strategies can be subdivided into area-wide or redeployable. The area-wide strategy would use a hub facility that tiesback and processes production from multiple prospects. The redeployable idea uses a floating production system to produce marginal fields for a relatively short time and then move to a new location for the same application.
Independence Hub
The current hub-and-spoke project under way is Independence Hub. Gas production is expected to begin this year at 1 bcf/d through the hub. Initially, 15 wells producing 50-70 MMcf/d of gas are expected to tie in. More wells will be added over time.
Schematic of the Independence Hub development.
Six companies have joined to develop multiple ultra deepwater natural gas discoveries in the Eastern and Central Planning Areas of the GoM. The Independence Hub will be on unleased Mississippi Canyon block 920 in 2,414 m (7,920 ft) of water. Block 920 is 177 km (110 mi) from the Mississippi River Delta and was selected for the permanently anchored host facility based on favorable seafloor conditions and proximity to the fields. Hub operator Anadarko Petroleum Co. expects first gas production in July 2007. Gas would come from Anadarko and partners Dominion, Spinnaker, Devon, and Enterprise Partners. Kerr-McGee was an original partner, but has been acquired by Anadarko.
Eastern Planning Area discoveries include Spiderman (DeSoto Canyon blocks 620 and 621), San Jacinto (DeSoto Canyon block 618), Atlas Northwest (Lloyd Ridge block 5), Atlas (DeSoto Canyon block 50), Mondo Northwest (Lloyd Ridge blocks 1 and 2), and Cheyenne (Lloyd Ridge block 399). Discoveries in the Central Planning Area include Jubilee (Atwater Valley blocks 305 and 349), Vortex (Atwater Valley block 261), and Merganser (Atwater Valley block 37).
A steel catenary riser would connect the topsides to 283 km (176 mi) of 20-25 cm (8-10 in) diameter flow lines from each wellhead to the hub.
Peak daily production rates for Independence Hub are 850 MMcf of gas and 4,250 bbl of condensate. The hub platform has an operating life of 20 years at a cost of $385 million. It has excess capacity to tieback 10 additional fields to cover future discoveries in this ultra deepwater area.
The project calls for 21 exploratory wells and installation of production tubing with a dynamically positioned completion rig for the anchor fields, and a moored semisubmersible drilling unit for the San Jacinto field. Subsequent stages involved sea bottom flow lines and production manifolds. This included a horizontal subsea production tree on each well, umbilical termination assemblies, pipeline manifolds, umbilical lines, flow line termination sleds, and connecting jumpers.
An export pipeline from the hub, called Independence Trail, will carry gas and condensate through a 61 cm (24 in) diameter pipeline 217 km (135 mi) to a fixed junction platform in West Delta block 68 in 34 m (110 ft) of water. Gas and condensate would go to shore from the junction platform at Port Sulphur, Louisiana.
Port Fourchon, Louisiana, will support heavy equipment, supplies, and crews for all Hub construction and production. Port Fourchon is 241 km (150 mi) northeast of Mississippi Canyon block 920. Heliport facilities at Galliano, Louisiana, would be used for crew transport and light supplies.
New technology
Independence Hub is designed to use 12 synthetic mooring lines to anchor the production facility; and the use of carbon rod technology in the dynamic section of the umbilicals is new.
Synthetic mooring lines are used on BP’s Thunderhorse platform. The main advantage of the synthetic lines is lighter weight compared to steel.
This graph shows the growing number of deepwater hubs in place over the last five years. Source: MMS.
The use of carbon rods in the dynamic section of umbilicals is new. Anadarko proposed using carbon rods in lieu of steel rods in the cross section of the umbilicals instead of steel rods. The length of the umbilicals is the driving factor for this plan because of the water depths involved. Tensions on the umbilicals will be high. Steel rods have a weight-to-strength ratio that is a disadvantage when compared to carbon rods with similar strength. The carbon rods will augment the axial strength of the umbilicals without adding significant weight. The carbon rods will be contained within the 15 cm (6-in) cross section of the umbilicals.
Na Kika
Shell Exploration & Production Co. and BP America Inc. developed the Na Kika project in the deepwater Gulf of Mexico in Mississippi Canyon block 474, 225 km (140 mi) southeast of New Orleans. Shell and BP each hold 50% of the project.
Shell’s Na Kika hub-and-spoke arrangement.
Na Kika encompasses five independent fields -- Kepler, Ariel, Fourier, Herschel, and East Anstey - which was developed using a centrally located, permanently-moored semisubmersible floating production facility. The Na Kika semisubmersible production facility is moored in 1,920 m (6,300 ft) of water. Individual wells are in waters from 1,764 to 2,134 m (5,800 to 7,000 ft) deep.
Kepler, Ariel and Herschel fields primarily are oil, while the Fourier and East Anstey primarily are gas. A sixth field, Coulomb, owned 100% by Shell and in 2,316 m (7,600 ft) of water, is tied back to Na Kika. At peak production Na Kika is expected to produce 110,000 b/d of oil and 425 MMcf/d of gas. Ultimate recovery is estimated at about 300 MMboe.
Shell was operator for the development phase of Na Kika, responsible for design, fabrication, and installation of the floating host facility and subsea production system, as well as the drilling and completion of 10 development wells. BP is the production operator, responsible for the operation of the host facility and the satellite subsea fields.
The semisubmersible is based on four steel columns, connected by four rectangular steel pontoons. The hull weighs 18,144 metric tons (20,000 tons) and provides 58,060 metric tons (64,000 tons) of displacement. The topside facilities measure 102 m x 83 m (335 ft x 290 ft). There are separation, dehydration, and treatment facilities designed to process 425 MMcf of gas and 110,000 b/d of oil.
Na Kika saw initial production in late 2003.
Canyon Express
The development which began the hub-and-spoke trend was Canyon Express. Total set up Canyon Express to bring three separate gas fields into production, and to transport the gas to Canyon Station treatment platform in Main Pass block 261. The wellheads are on the seabed at a depth of nearly 2,200 m (7,218 ft), and are connected to Canyon Station via a 92 km (57 mi) gas line.
The three gas fields serviced by Canyon Express are Camden Hills, discovered by Marathon Oil Co. in Mississippi Canyon block 348, Aconcagua, discovered by Total in Mississppi Canyon block 305, and King’s Peak, discovered by BP in Mississippi Canyon blocks 217 and 173 and Desoto Canyon blocks 133 and 177.
One Canyon Station export pipeline terminates at an existing platform, and three export pipelines terminate at subsea tie-ins with existing pipelines, all in Main Pass block 261. Total hydrocarbon reserves in the three fields at the time of development were estimated as high as 900 bcf of gas. However, no single field contains sufficient reserves to economically justify development. Planned maximum Canyon Express hydrocarbon flow rate is 500 MMcf/d of gas plus 1,500 b/d of condensate. First production was in 2002.
One important part of then-new technology implements at Canyon Express was inline multiphase flow meters to allocate production of all well streams prior to commingling. Until those meters were approved by MMS and accepted by the various operators, the problem of crediting production arriving at Canyon Station to the correct producer had not been solved.
Canyon Station is the production handling platform 97 km (60 mi) south of Mobile Bay, Alabama. It is a fixed-leg platform in 91 m (300 ft) of water. It was installed in mid 2002.
Gene Kliewer
Technology Editor
