A subsea intervention system with a standardized connector system, currently being developed by Paragon Engineering Services Inc., Houston, will allow remediation of subsea flow blockages from a surface vessel with a tool that connects directly to a manifold.
This tool will allow an operator to inject and circulate various chemicals into a single line to remove the blockage.
Paragon is currently working with Shell Offshore Inc. on equipment modification to meet the flow-assurance requirements for Shell's Serrano-Oregano developments in 3,400 ft of water in the Gulf of Mexico (see box).
At a substantial cost savings to Shell, Paragon is refining and standardizing an existing remediation system that was originally built for Shell's Mensa subsea development in 5,300 ft of water. The modified system addresses immediate requirements for the Serrano-Oregano developments while creating new avenues for ensuring production flow for multiple fields and applications.
Standardization
Standardized design and engineering allows the industry to further its deepwater development while helping to lower capital expenditures.
Flow-assurance technology is one area in which standardization promises to allow development of some fields that might have remained undeveloped, stymied by significant capital costs and risk management issues.
To date, industry has required a round-trip flow loop from a subsea facility to its host platform to accommodate pigging operations and to remove any blockage caused by hydrates, asphaltenes, or paraffin buildup. Other costly field-development options have included the design and installation of a separate coiled-tubing line or an umbilical specifically for removing asphaltenes.
With the expense of a deepwater flowline potentially representing one-quarter to one-third of field development cost, the new standardized remediation method will provide the industry another flow-assurance option with a nominal up-front cost and significant long-term value.
Industry wide, utilization of a standardized connector for a subsea intervention system designed for flowline remediation provides a significant cost avoidance for deepwater developments, improves field-development planning, and enhances asset management with greater control of production risk caused by flowline blockage.
Design efforts for this standardized system and similar research and development efforts are helping industry to solve the risk management problems associated with deepwater development while helping to speed delivery of new production systems to the frontier arena.
Serrano-Oregano
The system being readied for Serrano-Oregono can also be used on any of Shell's subsea systems that follow its current standardization philosophy. The system will have multiple capabilities for ensuring production flow, including the remediation of asphaltene, paraffin, and hydrate blockages.
Shell designed the original Mensa remediation system solely for hydrate problems, a critical issue for production from the Gulf of Mexico's deepwater installations.
The new system builds in greater flexibility and improved asset management with opportunities to employ a suite of remediation techniques at a very modest capital cost. A fraction of the size of the original Mensa connector, the subsea connection system in the new design will be about 10 ft high and weigh 8,000 lb. The Mensa manifold, which is very large and complex, has a 38-ft high, 14,000-lb connector system.
Paragon's project team has been on a fast track since early spring 2001 to complete the turnkey project for the new system. Paragon's role includes project management, basic design, detailed engineering, procurement, construction management, and system integration testing.
FMC Technologies Inc., whose predecessor company built the Mensa connector, is building the new connector.
The redesigned remediation system incorporates significant parts of Mensa's equipment, thereby saving money for Shell. Parts from Mensa include:
- Connector-support system for deploying the tool from a vessel with a moonpool.
- Remediation umbilical, 3 by 1-in. diameter metal tubes.
- Storage-deployment reel.
- Powered reel stand.
- Control panel.
- Surface mounted quick-disconnnect assembly, used to suspend the umbilical during remediation operations.
The new components include the new subsea connector, connector control box, and umbilical isolation-purge valve assembly box.
Tool operations
To operate the system, one holds the subsea connector tool in position over the moonpool on a dedicated spider beam while the connector is attached to the remediation umbilical, which is used to lower the connector assembly to the seafloor.
The connector tool lands and connects to the flowline manifold on the same utility connector hub initially provided for the Serrano-Oregano subsea pig launcher.
One then uses a remotely operated vehicle to actuate the connector and the umbilical's isolation and purge valves.
The upper end of the umbilical mates with a quick-disconnect device, mounted on the same spider beam. The inlets of the quick-disconnect device connect appropriate process-type equipment for the particular remediation activity required.
This activity may involve a combination of methanol circulation combined with depressurization for hydrate remediation or circulation of a paraffin or asphaltene solvent such as xylene or toluene.
After completing the remediation operations, one retrieves the system by reversing the deployment steps and procedures.
The author
Charles E. Horn is business manager for subsea and deepwater projects for Paragon Engineering Services Inc, Houston. He joined Paragon in 1997 and has more than 25 years' experience in the study, design, manufacturing, and fabrication of offshore-subsea oilfield production equipment. Horn also represents Paragon on the DeepStar flow-assurance committee.
Serrano-Oregano fields
Serrano
Serrano is in Garden Banks Blocks 516 and 472 about 220 miles southwest of New Orleans in about 3,400 ft of water.
Shell Offshore Inc. acquired the GB 516 lease in OCS Sale 104 in 1985 for $1.023 million and the GB 472 lease in 1989 in OCS Lease Sale 123 for $162,000.
It drilled the discovery well on GB 516 in 1996 and the discovery well on GB 472 in 1999.
The target gas and associated gas condensate reservoirs are the SE 40 and SE 55 sands at about 12,000 and 18,000-ft subsea. Shell expects an average net pay of about 80 ft and 110 ft, respectively, and a gross ultimate recovery of about 50 million boe.
The subsea system for developing the field includes two wells connected to a subsea-flowline sled that is tied back to the Auger tension-leg platform (TLP) with a single 6 by 10-in. pipe-in-pipe insulated flowline (see figure below).
Shell estimates total development costs to be about $120 million, excluding lease costs, and production to begin this month, with peak production rates increasing to 150 MMcfd in 2003 as gas capacity at Auger becomes available.
Oregano
Oregano is in Garden Banks Blocks 558 and 559 about 225 miles southwest of New Orleans in about 3,400 ft of water.
Shell Offshore Inc. acquired the GB 559 in OCS Sale 123 in 1989 for $177,000 and the GB 558 lease in 1989 in OCS Lease Sale 123 for $162,000.
It drilled the discovery well on GB 559 in 1999, and in the development it will target the oil and associated gas reservoirs in the K sands at about 19,000 ft subsea. The reserves contain a 35-37° gravity oil with a 1.08% sulfur content.
The subsea system, in 2,860-ft of water, has two wells connected to a subsea-flowline sled that is tied back to the Auger TLP with a single 6 by 10-in. pipe-in-pipe insulated flowline.
Shell estimates the development cost about $130 million, excluding lease costs. Production started last month and Shell expects a peak production of 20,000 bo/d in 2002, with ultimate recovery reaching 50 million boe.
