Gas production from the eastern Gulf of Mexico will start in 2007 from 10 deepwater fields tied into a floating central processing facility, Independence Hub, moored in about 8,000 ft of water.
Five of these fields are on leases acquired during Lease Sale 181 in December 2001. The sale was controversial and was reduced in size by nearly 75% because of environmental concerns in Florida (OGJ, Dec. 17, 2001, p. 32). Currently various federal legislative proposals seek to lease the acreage removed in 2001 (OGJ, Oct. 9, 2006, p. 27).
Fig. 1 shows the distances to shore for the blocks in the original lease sale.
Independence Hub ties together multiple deepwater gas fields lying in 8,000-9,000 ft of water that otherwise would be uneconomical to develop on a standalone basis. Initially 10 fields will anchor the project and produce about 1 bcfd to the hub platform, in about 8,000 ft of water on Mississippi Canyon Block 920. A high-pressure, 132-mile pipeline will transport the gas ashore.
The development has different owners for the processing platform, pipeline to shore, and producing gas fields.
Owning the hub is Independence Hub LLC, a venture of Enterprise Field Services LLC (80%) and Helix Energy Solutions (20%).
Anadarko Petroleum Corp. will operate the processing on the hub on behalf of the gas field owners that include Anadarko, Dominion Exploration & Production, Devon Energy Corp., Hydro Gulf of Mexico, and Murphy Oil Corp.
Enterprise Products Partners LP owns the Independence Trail pipeline that will transport gas ashore.
Initially, the platform will process production from fields shown in the accompanying box and in Fig. 2.
Anadarko is the operator of all of the fields except for two. Dominion operates San Jacinto, and Hydro operates Q. The company estimates that the area has a resource potential of more than 2 tcf.
Project highlights
Independence Hub semi will be moored 165 miles east of New Orleans in 8,000 ft waters. The fields are in the deepest water depths to date for producing fields. Also they have the longest tie-back flowlines, longer than 45 miles.
The project includes:
- Topsides with 1-bcfd processing capacity, largest in the gulf.
- 2.4 miles of mooring lines.
- Deepest suction pile installation.
- Largest monoethylene glycol (MEG) reclamation unit.
- Deepest pipeline inline future tie-in subsea structure.
- Longest single subsea umbilical order. Instead of steel rods, the umbilicals contain carbon rods that reduce the umbilical weight.
- The flowlines are 210 miles in total length, and the umbilicals contain about 1,100 miles of stainless steel tubing.
Field discoveries
According to the US Minerals Management Service’s Environmental Assessment for Independence Hub, November 2005, and OCS Report MMS 2006-022 the fields were discovered as follows:
- In 2001, Kerr-McGee Oil and Gas Corp. discovered gas at Merganser in 8,015 ft of water, reporting four reservoir sands. Kerr-McGee is now part of Anadarko.
- In December 2002, BHP discovered gas at Vortex in 8,344 ft of water, reporting 75 ft of pay. Anadarko now owns the field.
- In April 2003, Anadarko discovered gas at Jubilee prospect in 8,824 ft of water, reporting 83 ft of pay.
- In June 2003, Anadarko discovered gas at Atlas in 8,934 ft of water, reporting 180 ft of pay.
- In November 2003, Anadarko discovered gas at Spiderman in 8,087 ft of water, reporting 140 ft of pay.
- In January 2004, Anadarko discovered gas at Atlas Northwest in 8,810 ft of water, reporting 50 ft of pay.
- In April 2004, Dominion discovered gas at San Jacinto in 7,850 ft of water, reporting 100 ft of pay.
- In 2004, Shell Exploration and Production discovered gas at Cheyenne in 8,897 ft of water. Anadarko now owns Cheyenne
- In December 2004, Murphy discovered gas at South Dachshund in 8,340 ft of water, reporting 70 ft of pay. Anadarko now operates the field that has been renamed Mondo Northwest.
Not mentioned in the MMS report is the Q field discovered by Spinnaker Exploration Co. in mid-2005. Hydro bought Spinnaker in late 2005 and now operates Q. Water depth at Q is 7,925 ft.
Platform
The companies proposed to build the platform and pipeline in 2003, with procurement starting in 2004 along with the agreements for the ownership infrastructure, processing, and transportation. Topsides construction started in 2004, with hull construction starting in 2005.
The Atlantia Offshore Ltd. deep-draft semisubmersible hull has a 12-leg mooring system consisting of 9-in. polymer ropes. The hull displaces 45,800 tons and accommodates a payload of deck, facilities, and risers of 19,300 tons. It has a 105-ft draft.
Hull dimensions are 232 ft by 232 ft by 180 ft, with column dimensions of 46 ft by 46 ft. Pontoon dimensions are 38 by 26 ft.
The topsides operating weight of the deck and facilities is 10,250 tons. Each of the two decks is 140 ft by 220 ft.
Alliance Engineering designed the topsides that can process 1 bcfd of gas with 5,000 b/d of condensate and 2,960 b/d of produced water.
The platform accommodates twelve 10-in. and four 8-in. steel catenary production risers (SCRs). Gas export is through a 24-in. SCR. Initially the platform will have 5 production risers for the 10 fields.
Atlantia delivered the hull and mooring system under a lump-sum, turnkey engineering, procurement, and contraction (EPC) contract.
The hull, built in the Jurong shipyards in Singapore, left there on May 8, 2006, and arrived on June 23 at the Kiewit Offshore Services yard at Ingleside, Tex., which constructed the topsides (Fig. 3).
The Kiewit yard integrated the hull and topsides in September (Fig. 4).
Anadarko expects tow of the platform to its Mississippi Canyon Block 920 location to take place in late November.
Well completions
The projects initially will tie in 15 wells, with additional wells to come later. Anadarko expects production from each well initially to be 50-70 MMcfd. All wells target Miocene reservoirs.
The Transocean Deepwater Millennium and the Noble Amos Runner are the two rigs currently completing the predrilled wells. FMC provided the subsea wellheads and manifolds.
The 10 fields initially will have the following number of wells (Fig. 5).
- Atlas, 1.
- Atlas NW, 1.
- Jubilee, 2.
- Merganser, 2.
- San Jacinto, 2.
- Spiderman, 3.
- Vortex, 1.
- Mondo NW, 1.
- Cheyenne, 1.
- Q, 1.
The wells include a mix of single, two, and three-zone completions.
Anadarko wells are cased and perforated and completed with frac packs of 40-80,000 lb of 30/50 lightweight ceramic proppant and 8-gauge wire-wrapped screens.
The wells incorporate multiphase metering technology and other sensors downhole, incorporating sand detection technology, and developing an intelligent downhole instrumentation network of sensors (OGJ, Feb. 27, 2006, p. 51).
The fields include Roxar’s wet-gas meters for integrating different well streams from the multiple fields. Roxar says the meters allow accurate detection and measurement in real-time of the hydrocarbon flow rates and water production as well as flow-assurance input through the meters’ online detection of formation water.
In Anadarko’s operated fields, six wells have smart completions. Four wells have two completed zones while the remaining two have three zones completed.
Baker Oil Tools said the wells include its intelligent wells systems (IWS) placed in wells in 8,000 ft of water, the deepest water depth to date. The long 93-ft single subassembly included three IWS lines, one tubing-encased conductor (TEC) line, and two chemical injection lines.
Anadarko described a Spiderman three-zone well as having “smart” completions on two zones that would allow control of the zones from surface, while the middle zone would require rig intervention to open or close.
Anadarko said the wells are completed with either 5½-in. or 4½-in. 13-chrome tubing because of the CO2 content in the gas. The fields do not produce any H2S.
Wellhead shut-in pressure is about 6,000 psi, and the bottomhole shut-in pressures are 7,900-8,700 psi. Bottomhold temperatures are 132-172º F.
Pipeline
The Independence Trail Natural Gas Pipeline is a wholly owned affiliate of Enterprise Products Partners LP. The 134 mile, 24-in. pipeline connects the Independence Hub Mexico to an interconnect with Tennessee Gas Pipeline in West Delta Block 68. The West Delta 68 jacket was installed in July 2006 with the topsides integration taking place in October. The jacket is in 115 ft of water. Topsides weight is 850 tons and jacket weight is 350 tons
Allseas Solitaire completed the S-lay of the pipeline in August 2006 (Fig. 6).
The pipeline has a maximum operating pressure of 3,640 psi and a capacity of 1 bcfd. It has two subsea dual tees of 16-in. and 12-in. in water depths of about 6,500 and 4,500 ft, respectively, for future tie ins.
The 24-in. line consists of API 5L X-65 DSAW (double submerged arc welded) pipe coated with 14-16 mils thin film fusion-bonded epoxy (FBE) and an additional 2-3 mils rough coat FBE. Wall thickness and bare weight in air vary as follows:
- 1.350-in. WT, 326.9 lb/ft.
- 1.220-in. WT, 297.1 lb/ft.
- 1.070-in. WT, 262.3 lb/ft.
- 0.950-in. WT, 234.1 lb/ft.
Fields producing for Independence Hub
- Atlas (Lloyd Ridge Blocks 49 and 50, Lease Sale 181), Anadarko 100%.
- Atlas NW (Lloyd Ridge Block 5, Lease Sale 181), Anadarko 100%.
- Jubilee (Atwater Valley Blocks 305 and 349 and Lloyd Ridge Blocks 265 and 309, Lease Sale 166), Anadarko 100%.
- Merganser (Atwater Valley Blocks 36 and 37, Lease Sale 175), Anadarko 50% and Devon 50%.
- San Jacinto (DeSoto Canyon Blocks 618 and 619, Lease Sale 181), Dominion 53.3%, Anadarko 20%, and Hydro 26.7%.
- Spiderman (DeSoto Canyon Blocks 620 and 621, Lease Sale 181), Anadarko 45%, Dominion 36.7% and Hydro 18.3 %.
- Vortex (Atwater Valley Blocks 217 and 261 and Lloyd Ridge Blocks 177 and 221, Lease Sale 157), Anadarko 100%.
- Mondo NW (Lloyd Ridge Block 1, Lease Sale 116), Dominion 53.3%, Anadarko 20%, and Hydro 26.7%.
- Cheyenne (Lloyd Ridge Block 399, Lease Sale 181), Anadarko 100%.
- Q (Mississippi Canyon Blocks 960, 961, 1004, and 1005, Lease Sale 175), Hydro 50% and Dominion 50%.