EMAS Chiyoda Subsea’s John Meenaghan discusses challenges and solutions employed at three back-to-back tieback projects the company recently carried out in the US Gulf of Mexico
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The Lewek Constellation during reel exchange operations with the RB1. |
EMAS Chiyoda Subsea (ECS) completed the Big Bend, Dantzler and Gunflint deepwater subsea tieback developments for Noble Energy in the US Gulf of Mexico (GoM) in April 2016. The key to developing these challenging developments back-to-back was an innovative reel-lay concept featuring a portable reel delivery system, and a one-stop-shop project execution team approach.
The workscope included project management, engineering, procurement, construction and installation of eight pipeline end terminations (PLETs), five in-line tees and stalking, spooling and installing of over 160mi (258km) of 8in and 12in pipe-in-pipe (PIP) flowlines and over 56mi (100km) of umbilicals in water depths reaching 7200ft (2200m).
The offshore construction campaign began in May 2015 when ECS performed record-breaking pipelay trials for the newly launched flagship, Lewek Constellation. ECS laid 3.2km of 16in rigid test pipe with 28mm wall thickness and two PLETs in 7368ft (2250m) water depth. The installation required 632-ton of top tension, setting a world record for the highest tension ever experienced for rigid, reeled pipe.
Innovative reel delivery system
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Reel exchange offshore. |
The fast track nature of these three developments required an innovative execution plan to bring all three developments online in under a year. Conventional reel-lay operations require reel-lay vessels to transit back and forth to the spool base to replenish the reels with the PIP and steel catenary riser (SCR) stalks. Welding, non-destructive testing and field joint coating of the stalks are critical path activities with known degrees of associated risk.
ECS utilized a portable reel concept allowing the Lewek Constellation to stay offshore in the project location while a dedicated barge, RB1, shuttled between the spool base and the pipelay location delivering loaded reels in exchange for empty reels. Reel transfers (four empty for four full) have been executed in under 24 hours on location. The result is a more efficient use of the pipelay vessel during the campaign removing reeling from the critical path and minimizing vessel transit time. This effectively decouples the Lewek Constellation from the spool base and takes the pipeline fabrication off the critical path by controlling welding and inspection conditions onshore in a controlled environment.
Pipelay campaigns
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The PLET handling system. |
Between Q2 2015 and Q4 2015, the Lewek Constellation conducted more than 38 heavy lifts between 900- and 2250-tonne transferring rigid pipe reels for the Big Bend, Dantzler and Gunflint projects as well as lifting a topside module onto an offshore platform. In total, the RB1 made 10 trips between the spool base and the vessel.
The Big Bend project is a single tieback with a bidirectional PIP flowline loop and insulated SCR from the Big Bend wells to the Thunder Hawk host platform facility. The pipe diameters included an 8in insulated pipe carried in a 12in outer pipe with the distinction of being the heaviest PIP system ever deployed in the world using the reeling method.
The Dantzler field, co-developed with Big Bend, consists of dual tiebacks with bidirectional PIP flowline loop, including a daisy-chain configuration connecting both Dantzler wells at Mississippi Canyon (MC) 782 and an insulated SCR to the Thunder Hawk host platform facility at a water depth of 6561ft. A bidirectional PIP flowline segment then connects the Big Bend and Dantzler fields forming a pigging loop through both systems in either direction. This co-development of flowlines is known as the Rio Grande Loop, and includes the Big Bend and Dantzler flowlines, SCRs, and hull piping up to the boarding valve.
The Gunflint field, in MC 948, consists of dual bidirectional insulated PIP flowlines and two wet-insulated SCRs along with umbilicals and subsea systems between the Gulfstar 1 spar in MC 724 and the two production wells.
Challenges
Early in the project, ECS received new soil data for the Dantzler field and it turned out to be softer than initial assumptions taken from the Big Bend project. This led to a determination that both Big Bend and Dantzler PLET mudmats would require wings to provide more stability to the PLETs and subsea structures on the seabed. While the Lewek Constellation could easily handle the weight and size of Gunflint’s PLETs and in-line sled, when the wing structures were added for Big Bend and Danzler, the PLETS became among the heaviest ever installed in the world. This required ECS to replace the existing 60-ton PLET handling device (PHD) with a 100-ton PHD for deployment of the heavier PLETs. Fortunately, the Lewek Constellation has one of the largest moonpools in the industry. The wings extended from the structures once they were lowered to the seabed through the 8m x 19m moonpool. Also equipped with a 3000-tonne Huisman crane and dual 600-tonne A&R system with a tri-plate that enables abandonment and recovery up to 1100-tonne, the vessel is able to lower very heavy structures or pipe product to the seabed in excess of 13,000ft (4000m) of water.
Throughout the pipelay campaign, ECS also encountered extremely challenging 3-4 knot loop currents. The Lewek Constellation was able to hold her position in currents greater than 3 knots, plus heavy seas and strong winds while installing SCRs at Big Bend. Equipped with nine thrusters and powered with eight main and auxiliary generators controlled by a Kongsberg Maritime dynamic positioning (DP3) system, the effects of weather were minimized by the ability of the vessel to adjust during installation sequences and continue working in very high current conditions.
Technology and assets
Every ECS asset and facility available in the US GoM region was used over the course of the project. Subsea structure fabrication and linepipe production took place at EMAS Marine Base (EMB); offshore survey and light construction operations were carried out with Lewek Falcon and Ambassador, umbilical installation with Lewek Connector, rigid pipeline installation with Lewek Constellation supported by RB1, and the installation of subsea structures, flying leads and rigid jumpers with Lewek Express.
The one-stop-shop approach applied to these three back-to-back tiebacks in combination with the innovative reel delivery system and unique vessel design were all key elements in the successful execution of the campaign.
Noble Energy brought the Big Bend and Dantzler fields online in October 2015, with Gunflint starting production in July 2016, all three within budget and ahead of schedule.
John Meenaghan joined EMAS Chiyoda Subsea in 2011 as vice president Global Operations. He has over 40 years’ experience in construction and installation, and is an industry pioneer in reel-lay. He is responsible for all offshore and onshore construction activities, including operational oversight and management of senior level offshore construction managers, supervisors and work forces. He was directly responsible for leading the transitional efforts from build to operations for the Lewek Constellation, the Reel Barge 1 and the two spool bases (Ingleside, Texas, and Gulen, Norway). Prior to joining the company, Meenaghan also served Santa Fe, Technip, Brown and Root, and Subsea 7 respectively over a period of 35 years.
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