Twenty years after it came online, the UK’s longest serving permanently-moored FPSO has been given a new lease on life. Elaine Maslin reports on the extent the UK’s largest offshore project in 2012.
When production from the central North Sea Gryphon field came online in October 1993, it was seen as a success. In a tough economic climate, operator Kerr McGee cut 35% of the capital cost and achieved first oil almost three years faster than planned, by choosing a floating production, storage, and offloading (FPSO) vessel, the Gryphon Alpha, instead of a fixed platform (OE: October 1994).
The Gryphon Alpha, stationed 282km north-east of Aberdeen in 112m water, in Block 9/18b, was the North Sea’s first permanently moored FPSO. Of the first 12 wells—7 were for horizontal production.
Kerr McGee had expected the 90,000-tonne vessel to remain on station for its estimated 15-year field life By 2011, the vessel had been producing for 17 years. Maersk Oil North Sea UK took ownership, after it had bought Kerr McGee’s UK assets in 2005.
The Gryphon Alpha was upgraded in 2003, primarily to enable it to process fluids from the Maclure and Tullich reservoirs. However, obsolescence was becoming an issue. Equipment was getting harder to support and plans were underway to replace multiple systems.
Then, on February 4, 2011, disaster struck. The vessel broke four of its 10 anchor chains and drifted off station in a storm. Extensive subsea infrastructure was damaged, including subsea risers and riser bases, several of the 18 mid-water arches, and flowlines to two well centers. The Gryphon Alpha itself also sustained damage, requiring it to be drydocked.
It was a blow. But the result was the Gryphon Area Reinstatement Project (GARP)—an intensive, 2½-year campaign, involving simultaneous design, procurement, rebuilding, and installation, to reinstate the now heavily overhauled FPSO and subsea infrastructure. It was the largest offshore project in the UK North Sea during 2012, with first production in May this year.
Subsea equipment
The first major piece of work was the removal of the damaged subsea infrastructure, carried out over six campaigns between July 2011 and March 2013. First, about 34 tonnes of oil was recovered through flushing to 34ppm (parts per million) of oil topside, using the temporarily-reconnected FPSO and support vessels.
Next, 36.6km of pipeline was removed, comprising 3600m of risers, 1920m of umbilical risers, 21,640m of seabed pipelines, and 9520m of seabed umbilicals. In addition, six riser bases and seven mid-water arches were removed.
Onshore contractor, TWMA, handled, cleaned and recycled 95.3% of a the 2.5million tonne of recovered materials.
Reinstatement
The removal of the subsea infrastructure gave Maersk an opportunity to re-engineer and simplify its subsea facilities.
Instead of replacing the seven midwater arches, Maersk designed a new subsea layout using three, 98-tonne, tethered midwater arches, built at the Nigg Yard, and three risers with buoyancy modules. This reduced manufacturing and offshore lifting scopes.
The number of gas lift risers was reduced from eleven to two, with distribution via new subsea control modules, which replaced the complex, direct control arrangement with a simpler multiplex system. The layout of flowlines and umbilicals was also consolidated.
In normal circumstances, the work involved would have taken 4-5 years, says Maersk’s Shona Campbell, project manager, subsea. On GARP, conceptual engineering, front-end engineering and design, procurement, and construction, involving more than 70 vendors and multiple contractors, was all carried out at the same time.
Technip used the 15 dynamic risers, two dynamic and two static umbilicals (manufactured by DUCO Dynamic Umbilicals, Newcastle), 11 flexible flowlines (from NOV Flexibles) and other subsea equipment,using Skandi Arctic and Wellservicer vessels to install. Fugro provided survey and ROVservices from the Fugro Symphony, as well as ROV services for four Technip DSVs (dive support vessels).
Maersk used 22 diverless hull connectors, supplied by FES International, to install the risers, which was trialed onshore before the offshore campaign. In total, about 39km of flexible flowlines, umbilicals and risers were installed, as well as 3000-tonne of structures, the mid-water arches and 21 wells hooked up, utilizing 703 vessel days.
FPSO Gryphon Alpha
The Gryphon Alpha arrived in dry dock at Damen Shiprepair Rotterdam (Schiedam) on June 27, 2011. Superficial cracks, not identified offshore were found, enabling a more thorough overhaul than could have been achieved offshore, with 550-tonne of steel replaced. Neil Smith, offshore health, safety, security, environment, and quality (HSSEQ) specialist, Maersk, says: “Any vessel, through natural vessel movements, is subject to stresses, fatigue, and corrosion. You can deal with most of this offshore, but it is very challenging, time consuming, and costly. When we had the opportunity to have the Gryphon Alpha in the yard we were able to do a lot of that work.”
The vessel’s three Hydralift hydraulic cranes were removed and refurbished with upgrades addressing obsolescence issues. New loading alarms and boom-tip cameras were also fitted. In addition, new bumper bars were installed to protect high-risk areas during lifting operations.
A new, taller, inert gas tower, including high velocity vent valves, was installed, standing 24m above the production deck, to increase its distance from the vessel. Lay down areas were expanded and improved, by replacing a metering skid with a new, smaller, multi-phase system, and removing an old dehydration unit and produced water systems. A new high-pressure flare-knockout drum was also installed, replacing two vessels used previously, also improving the footprint.
A strong theme of the replacement equipment was a greater ability to capture, access and use data from the process and marine systems.
The Solar Turbines gas turbine control systems were replaced with a Turbotronic 4 system, including new programmable logic controllers (PLCs), enabling more information about performance to be accessed, including analyzing alarms and ability to access data from a remote terminal at the bridge.
The Provox process control system (PCS), which was becoming harder to maintain due to obsolescence, was replaced with an Emerson Delta-V system. This meant increased access to data for onshore teams, for monitoring and reviewing trends. Due to a change from switches to transmitters, the application of plant inhibits will also be reduced through improved monitoring.
One of the biggest pieces of work was the installation of a new secondstage separator, says Marc McAndrew, Gryphon asset process engineer. The existing second-stage separator had a design pressure of 3.1 Bar(g) but the upstream first stage and test separator systems wererated to 12.9 Bar(g) and were operating in the 9-10 Bar(g) range. A fully rated replacement vessel, including new pressure safety valves, was installed at 12.9 Bar(g) design pressure.
This was supplemented by a new HIPPS (high-integrity pressure protection system), with two, 16in. Mokveld valves on the production header, two 6in. Mokveld valves on the test header, and an intelligent logic solver from Yokogawa. This was the result of analysis, which highlighted a potential to overpressure the first stage and test separator, due to de-packing of flow lines potentially at gas lift pressure.
In addition, a nucleonic density profiler was added to the second-stage separator, allowing increased visibility of the separation performance, on- and offshore, specifically around the build-up of emulsions, so early proactive action can be taken, says Alan Simmonds, controls engineer.
The new second-stage separator and the HIPPS, were the result of a high level of design work, says Neal Gray, head of technical assurance, Maersk.
“The whole system is the way we control the risk of overpressure in the first vessel in the process train,” he says. “With the HIPPS system we can monitor it and, if it happens, shut it down quickly and then control how fast it starts up.”
The Gryphon Alpha’s Lintott direct hydraulic well head control panel, which consisted of a manually operated panel inside the turret and had become obsolete, was removed. Its functionality was absorbed into the existing electric-hydraulic system, feeding into a master control station, that has greater flexibility to be reconfigured.
Obsolescence also resulted in a new cargo system, Kongsberg’s K-Gauge. The cargo pumps, valves and chemical inject skid were fully refurbished and a new fiscallyrated offload metering system introduced.
All at-risk areas, including the forward blast wall, that protected a temporary refuge area, were brought up to a 90-minute jet fire (J90), standard, when previously only the risers and the emergency shutdown valve were covered. All vessels were reclad in Foamglas and a Terostat outer cover. Insulation around pipelines was also upgraded to hard foam, instead of fiberglass wool.
The vessel’s flare tower was going to be replaced, but it was refurbished, and additional lights installed. New life boats, adhering to recently increased personnel size specifications, were also installed.
Marine systems
Work had already started on replacing the Gryphon Alpha’s dynamic positioning (DP) systems, with an upgrade to the Kongsberg thruster control and vessel automation system. The vessel had a Kongsberg Simrad vessel control and Simrad dynamic positioning system, which has been upgraded to K-Pos thruster control system, K-Chief vessel automation system and K-Safe safety module, or emergency shut down and fire and gas system. The upgrade to K-Safe included replacing the vessel fire detection system with a new Autronica fire panel and detectors. Maersk also upgraded the position reference systems, giving Gryphon Alpha triple redundancy.
The thruster control system now has full redundancy, so that if there is any single failure, no matter how significant, the vessel will have sufficient thruster capacity to remain on station.
In a situation such as a Force 8 gale, the power systems can be split, separating process power (two Solar Mars gas turbines) from marine systems (five marine 3MW diesel generators). The marine systems can also be split, so that at least two thrusters are always available. The system went through a full failure mode analysis and sea trials, prior to deployment.
Rolls Royce at Ålesund, Norway, also overhauled, recertified, and refitted Gryphon Alpha’s thrusters.
Tanks
The FPSO has a storage capacity of 525,000 bbl in 12 inert, gas-blanketed cargo tanks, with offloading via a 20in. hose to shuttle tanker. These, and the ballast tanks and anodes, were corroded and were due to be refurbished offshore. Instead, they underwent a more thorough inspection in drydock, and were blasted, cleaned, had welds repaired, and recoated in drydock.
Mooring system
When the vessel was first installed, the mooring system was rated to the latest 1989 standards. The rating has now been increased to 2010 standards, increasing the minimum break load (MBL) of the chain to 858-tonne—a 17% improvement on the old R4 chain.
To meet new codes, including DNVOS- E301, the damaged 10-point mooring system was replaced, upgraded, with new mooring chain forged by Spain’s Vicinay Cadenas. Fair leads were also increased to an MBL of 858-tonne.
The Vryhof Stevpris anchors were overhauled and new Smit towing brackets and chocks fitted fore and aft, for vessel positioning during hook-up.
The 134 cylinder bearings (67 sets of two) on the 4000-tonne, 20m-diameter, hydraulically operated turret amidships, were overhauled, and the carousel steelwork and drag chain overhauled. The turret turning and locking system was also replaced, due to obsolescence, with a new programmable logic controller system with human-machine interface, to enable the operator to see more data.
The reality is that much of the work carried out between February 2011 and April 2013 in drydock—not all of it outlined here—was planned before the incident. But, it would have been carried out offshore, during a time which has seen multiple periods of bad weather and the grounding of part of the North Sea’s helicopter fleet, due to two ditchings in 2012, making logistics particularly difficult.
The extent of the repairs meant the vessel was able to achieve class renewal, which had been scheduled for 2016.
Scott Taylor, installation support engineer, Maersk, says: “It would have been challenging to see Gryphon Alpha out of commission much further than that. Now, as long as wells are producing, we should see Gryphon Alpha through in to the future. It was all about doing work now that was going to future-proof us.”
Tow-out
On May 27, 2012, the drydock was flooded and Gryphon Alpha floated out. Sea trials were in the southern North Sea during August, and mooring hook-up and riser pulling during September and October 2012.
Commissioning and hook up of marine systems started October 2012, including failure mode and effects analysis, a process limited by the allowable number of persons on board (130), and not helped by poor weather and the limited helicopter service. Topsides commissioning then led up to May 2013, for first production.
“We checked everything in triplicate— flanges, nuts, lines, piping and instrumentation diagrams (P&IDs),” says Stuart Oswald, offshore installation manager, Maersk.
The P&IDs had all been updated to “as built” and line walked, the process integrity register updated, as was the alarm and trip register, the safety and integrity level register—in fact all documentation—in addition to DNV verification.
“From Martin Rune Pedersen [managing director, Maersk Oil North Sea] to Pers Skrumsager, the operations manager, the mind set was that we were not going to start until we were ready,” says Oswald.
Before first oil the entire team took “24 hours out for safety.” All staff, both those who had been with the vessel before February 4, and after, undertook training on the new and retained systems.
A vessel was hired with the same DP system as Gryphon Alpha for the crew to train on. Emergency situation scenarios were also introduced, with every potential emergency scenario worked through, training carried out, for staff, vendors and contractors, and procedures recorded in the Environmental Health and Safety Plan.
Production of Gryphon Alpha, targeted at 20M bbl/d restarted in May, without any leaks, and is currently “exceeding expectations,” says Oswald, with additional wells due online by the end of the year.
The third gas compressors is scheduled to come online this month [Sept] and water injection systems were due to be commissioned as we go to print.
The future
While the short term aims are to make the Gryphon Alpha work optimally and stably, Maersk has a long term plan for Gryphon Alpha.
New 4D seismic was shot over Block 9 in 2011, while the vessel was off station—work that had already been planned in cooperation with other operators in the area.
The Gryphon reservoir is in shallow Eocene sands and has heavy crude oil, at 22°API gravity. Maersk has developed expertise in injectile sands, which it has been working on in the Gryphon area since 2003.
During the reinstatement project, Maersk also carried out a drilling campaign at the Tullich field, and, in July, it started drilling a new well at Gryphon, using the Sedco 704 semisubmersible. Another well is planned on Maclure, using the WilPhoenix semisubmersible. Maersk is still working up its 2014-15 drilling program.
Doug MacLeod, development manager, Quad 9, Maersk, says: “There are certainly a lot more opportunities in the area. It’s very exciting. There is a lot of potential—Gryphon is going to need more subsea infrastructure.”
Gryphon ownership
Maersk Oil operates the Gryphon field and the Gryphon South field (discovered 1987) in partnership with Sojitz. Gryphon field equity share: Maersk 86.5%, Sojitz 13.54%, South Gryphon field equity share Maersk 89.875, Sojitz 10.125%.
Maersk also operates the Tullich and Maclure fields (both discovered in 1991, with first oil in 2002), which tie in to Gryphon.
Maersk has a 38.2% equity share in Maclure, with partners TAQA Bratani (37%), Apache (17.2%), and Enterprise Oil (7.6%).
Tullich is 100% Maersk-owned and operated.
With thanks to, alongside those quoted, Rob Waugh, senior piping engineer, Paul Baker, environment manager, and Fred Toal, naval architect. OE
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