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Subsea Tieback Expertise

The topside expertise to support your subsea tiebacks.


With subsea tiebacks, what goes on above the surface is just as important as what is happening beneath it.

Since the early 1990s, EDG has been executing topside modifications to accommodate deepwater subsea tiebacks. We provide systems engineering and critical physical interfaces to ensure the success of the overall project. Our engineers and technicians are committed to a job from concept selection through Front-End Engineering and Design (FEED), Detailed Engineering to offshore commissioning and startup.  At EDG, our hands-on approach to service means ease of operation and getting the help you need when you need it – in any phase of the project.


Projects Completed


Long Distance, Low Temperature Gas Subsea Tieback 

EDG was tasked with the FEED and DE for a two-well, 56-mile gas tieback to a deepwater spar. We were selected to execute this project because of our familiarity with the host facility and our direct relevant experience on another subsea tieback project. Our scope of work involved all project facets, including engineering of the topside modifications and equipment additions, detailed design, procurement support, fabrication inspection, construction management both onshore and offshore, as well as regulatory support. The new gas train features a Taurus booster compressor and a new stainless steel vent system to withstand the sub-zero temperatures during depressurization activities. Temporary production facilities were added to accelerate startup.


Subsea Tieback to Deepwater TLP 

EDG is providing the engineering, procurement support and execution planning of a multiple well deepwater subsea tieback to a TLP. Topside facilities for this subsea tieback include pig traps, topside chokes, flowline heaters, multiphase meters, pigging pumps, chemical injection equipment and controls. Despite its unique challenges, we are implementing one of the first ever Gulf of Mexico uncertainty-based allocation systems for oil, gas and condensate production.


Subsea Tieback/Module Addition Project

EDG executed the Detailed Design phases of two subsea well tiebacks to Ewing Banks 873 “A” Platform via dual 6-inch insulated flowlines. To accommodate the two subsea wells, located in 1800 feet of water, a three-level production module measuring approximately 105 feet by 25 feet was added to the platform to process the incoming production. EDG designed the production facilities which consist of high-pressure pipeline risers and pigging system, four vertical centrifugal degassing vessels, a vertical shell and tube heat exchanger, a production separator and hydrocyclone. Additional module equipment included a plate and frame heater, a combination electrostatic oil treater and oil storage tank, and plate and frame coolers. Platform additions included larger heat medium pumps and an additional LACT charge pump. Subsequent equipment upgrades designed to increase production capacity included a larger low pressure relief scrubber, a second flare tip, a third sales gas compressor, a second vapor recovery unit and a fourth 1000-hp pipeline pump.


Three-Well Subsea Tieback to Weight and Space-Constrained Spar

EDG championed this project to provide the FEED and DE of the topside modifications and equipment upgrades for a three-well tieback to the Devils Tower Spar. Located in 5600 feet of water, weight and space limitations presented unique challenges during the FEED phase of the project. Nonetheless, our innovative and detail-oriented engineering professionals completed the topside modifications well within topsides weight targets. The team leveraged concepts from ANSI B 31.3 to minimize the weight of high-pressure piping and stay within the aggressive weight limits for the project. 

A crude-to-crude exchanger was installed to free-up heat from the waste heat system for use in the new subsea flowline heaters without adding supplemental heaters to the existing facilities. The heat exchangers were carefully selected to provide adequate heat for both the low and high GOR cases while minimizing the pressure drop for the high GOR cases. A pipe-in-pipe design was specified for the exchanger to circumvent low-temperature concerns on relief valve outlets.  


Deep Water Field Developments

In 2004, EDG began providing operations support for two deep water spars. Since our initial involvement, we have assisted on a total of six subsea tiebacks to these spars. We provided FEED and detailed engineering, including installation and startup support for the topside facilities.The new facilities featured boarding valves, multiphase metering, manifolds, chemical injection equipment and control systems. Many of the tie-ins were extended to the top deck to simplify the multiple piping connections and to reduce shut-in time.


Field Development Solutions for Deepwater Prospects

EDG has also executed conceptual engineering and alternatives analysis for several subsea tieback studies. We offer extensive field development experience in investigating the feasibility of a tieback versus a local host platform, developing costs and schedules and performing associated risk assessments. Recent experience includes creating field development alternatives and performing risk assessments of the costs and schedule for the Blind Faith Deepwater Field Development. In addition, EDG studied the feasibility of a subsea tieback versus a local host platform for the Champlain Deepwater Field Development. Semi-submersible, FPS, TLP and mini-spar options were among those studied, as well as a subsea tieback to several host platforms.


Underwater Subsea Separation System

EDG was awarded with designing the subsea processing system that would potentially be fabricated for a future subsea field. This system would be designed to produce oil, gas and water.  The design involved a three phase horizontal separator that would need to separate the production stream into three separate streams: gas, oil and water. The future separator system would need to include a sand removal system to periodically remove sand from the separator. The project involved the coordination of gas tolerant pumps that would transport the oil stream to a host facility and a single phase pump would be utilized to inject the produced water stream into a well for disposal. A sand handling system comprised of a desander/accumulator to dispose of any sand production that was removed from the separator was needed and the gas stream to naturally flow to a host facility for further processing and use and reinjection.

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