Islay tieback turns up the heat

Meg Chesshyre
Thursday, December 1, 2011

Total's UK North Sea Islay tieback, a gas condensate field with challenging flow assurance issues for the management of hydrates, is being used as a pilot for what is being hailed as the world's first electrically trace heated pipe-in-pipe system. Meg Chesshyre reports.

Total's R&D group reviewed several solutions for flowline optimization for its UK North Sea Islay tieback and, from among the different technologies available, identified Electrical Trace Heated Pipe-in-Pipe (ETH-PiP) as the most viable option, with higher energy efficiency when compared to the direct electrical heating systems (DEH) and hot water circulation (HWC).

The sophisticated cable application machine at Technip's Evanton spoolbase allows simultaneous application of the trace heating and fibre optic cables during the standard pipe in pipe insertion operation. Four spirally wound trace heating cables, and two spirally wound fibre optic temperature monitoring cables are incorporated in the Islay pipeline.

Following extensive qualification trials, the decision was made to ‘industrialize' the electrically heated pipe-in-pipe (ETH-PiP) system which had been developed by Technip in collaboration with Total. ‘This development could have significant implications for the oil & gas industry,' says Jean-François Cam, Total E&P UK's subsea projects manager. ‘We believe it is a promising option for the industry as its power requirements are significantly less than DEH or HWC. In terms of size, Islay is the perfect pilot,' he adds.

By way of comparison, he points out the DEH-PiP system currently used on the Shell/BP Na Kika field in the Gulf of Mexico (OE July 2003) required five to ten times more power than ETH-PiP. ‘With the Islay project's ETH-PiP, the electrical efficiency is over 85% and the heat losses are minimised as the heating source is 100% under the insulation, so the overall efficiency of the system is greater.'

Located in 122m of water in the northern North Sea and with reserves of 17 million boe, Islay is being developed as a single well tieback to the existing Forvie North manifold, itself linked to the Alwyn North field centre. It will be tied back by a 6km, 6/12in pipe-in-pipe system, which incorporates the ETH-PiP system to help deal with hydrate management. The PiP 6in flowline is made of super duplex steel covered with a proven high-performance passive insulation material and ultimately protected by the outer carrier pipe.

To incorporate the four spirally wound trace heating cables, and two spirally wound fibre optic temperature monitoring cables, Technip developed a sophisticated cable application machine which allows simultaneous application of the trace heating and fibre optic cables during the standard pipe-in-pipe insertion operation.

Located at the company's Evanton spoolbase in Scotland, the machine completed the manufacture of the Islay pipeline in August. Technip's Apache II pipelay vessel was mobilising late November for the pipe's planned 4Q installation in the field, weather permitting.

Because it is a pilot, the electrically heated system is not permanently connected, as this would have required a new 17km umbilical from the Dunbar platform back to Forvie. During commissioning and after the field start-up the system will be powered and tested with the support of an ROV intervention vessel, and its performance will be monitored by real-time fibre optic temperature monitoring along the 6km length. Given satisfactory performance, Total says it can still make it a permanent connection to the main system at a later date. The heating cables have a design life of 20 years.

ETH-PiP has been developed by Technip over the last 10 years, working on a qualification process with Total for the last few years. Now in the industrialization phase, this low power solution is said to be up to 10 times more efficient than direct electric heating and thus require significantly less topsides space, which can be critical in brownfield developments. The pipe-in-pipe dry insulation also enhances efficiency.

Last piece of the jigsaw

The world-first field deployment of ETH-PiP on Islay, albeit as an addition to the base case flow assurance solution, represents ‘the last piece of a SURF technology jigsaw foreseen since the late 1990s', according to Technip UK's Islay project manager Rob Fisher. When operational, he adds, this project will ‘once again demonstrate the criticality of the North Sea in providing an arena for transfer of ground-breaking technology to the worldwide subsea industry'.

Looking back, Fisher points out it was the twin technology challenges of deepwater and flow assurance that prompted his company to embark on a decade of R&D focused on expanding the application of reeled pipelines and in particular PiP systems.

‘Notable achievements were made, namely the installation of reeled PiP steel catenary risers (SCRs) in the Gulf of Mexico, the world's deepest water PiP installation and the most thermally insulated PiP using passive insulation systems,' he says. ‘This latter application was installed for the Total Dalia project offshore Angola, and until recently marked the zenith in the use of PiP technology using such passive insulation alone to solve flow assurance problems.'

In a separate, innovation flow assurance exercise last year the giant suction hopper dredger Cristobal Colon was deployed for "seabed conditioning along the route of the Islay pipeline.

Anticipating the market would require ever more thermally efficient PiP systems, and realising that Dalia would be close to the threshold for passively insulated PiP products, Technip had some years earlier embarked on the development of a heated PiP product. The company chose to focus on electrically trace heated PiP, seeing it as a low power solution which also complimented reel-lay installation techniques.

Technip completed its R&D programme in 2003. ‘But the anticipated requirement for more demanding flow assurance applications did not immediately materialise, with market needs being fulfilled by passive insulation alone or, in a limited number of cases, the use of direct heating technology,' recalls Fisher. However, with Total Group working closely with Technip and others from 2009 to advance the ETH-PiP concept, subsea design solutions emerged to enable its pre-qualification. Extensive onshore industrialisation followed Total's subsequent award of the Islay Development Project to Technip, including major infrastructure enhancements at the Evanton spoolbase to accommodate ETH-PiP assembly.

Seabed conditioning

Jean-François Cam points out that ETH-PiP is being deployed in addition to another innovative flow assurance solution involving seabed conditioning, and is therefore not essential to the success of the project. ‘A survey of the pipeline route showed five separate depressions, each of which could create a liquid trap requiring complex methanol injection points to be installed subsea,' he notes. Total decided to reshape the seabed so that it had only one low point.

This work was carried out in October 2010 by Jan de Nul's Cristobal Colon, the world's largest suction hopper dredger. The 263m-long vessel achieved the target seabed profile with vertical tolerances of less than 300mm to ensure free draining of liquid. A midline methanol skid has been installed at the remaining low point so that methanol can be injected to counteract hydrate formation. Islay also has a fully integrated high integrity pipeline protection system (HIPPS), supplied by DrilQuip.

Another Islay innovation is the deployment of the first fibre optic control umbilical to be used anywhere in the Total Group. This allows for the separation of electrical power and control signals between the Forvie manifold and each end of the production flowline, and eliminates the risk of interference from the electrical power also being transmitted through the umbilical.

The umbilical and production pipeline from the Islay well to the Forvie manifold will be installed parallel to each other about 50m apart. The production pipeline will be laid along the seabed conditioned areas to the Islay well, with rock-dumped protection along its entire length. The umbilical will be trenched and backfilled with mattressing for protection where the umbilical ties into the PLEMs and midline methanol injection point. Once the pipeline has been installed, it will be tied into the existing Forvie manifold using a diving support vessel.

Islay is located 3km to the east of Total's existing Jura gas field in UK block 3/15 and Norwegian blocks 29/6a&c. Total has a 100% stake in the field. OE

Categories: Equipment Europe Flow Assurance

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