Overcoming obsolescence issues with minimal disruption

29 November 2011

CEE reports on how TOTAL E&P UK has succeeded in safely upgrading a number of vital systems on two of its Alywyn Area fields platforms.

TOTAL E&P UK is one of the main oil and gas operators on the UK continental shelf. Its portfolio includes operatorship of the Alwyn Area fields, the high pressure/high temperature Elgin and Franklin fields and the St Fergus Gas Terminal, together with a number of non-operated fields.

The North Alwyn complex, located on the UK continental shelf 440km northeast of Aberdeen, commenced production in 1987. The Dunbar platform located 22km to the south of the North Alwyn complex exports oil and gas to North Alwyn via a multi-phase pipeline, which commenced production in 1994.

Dunbar is a minimum-facilities platform with minimal process facilities, a drilling derrick and living quarters. Electrical power is supplied from the North Alwyn generators via two submarine cables. Alwyn Area produces approximately 100,000 barrels of oil equivalent per day.

A number of obsolescence issues led the company to call on Rockwell Automation to supply engineers, components and support for a number of systems upgrade across the two platforms, with the majority of the work taking place on the Dunbar facility.

The upgrade encompassed a number of systems: the emergency shutdown (ESD) system, the fire and gas (F&G) safety system, the Process Control System (PCS) System and the vibration-monitoring systems.

The main challenge faced by the engineers was the safe delivery of an upgraded control and safety system with minimal disruption to operations. There was a limited window of opportunity in which to complete the work, with just two opportunities to do the upgrades. The first was during a planned shutdown period – normally two or three weeks in the summer period, and the second was through concurrent replacement of running components and infrastructure elements prior to the shutdown.

The main objectives were to replace system components to overcome spurious trips and major obsolescence issues, while having spares available until at least 2020; to provide the facility for future remote operation of Dunbar from North Alwyn; implement a cost-effective upgrade with minimal risk to production and to complete the upgrade with no risk to the safety of the platform, personnel or the environment.

The strategy for the upgrade comprised a number of individual, but not mutually exclusive steps. The PCS system was upgraded prior to the shutdown, being installed in tandem with the existing system to maintain production capacity. The F&G system was also upgraded prior to the shutdown and the ESD solution was upgraded during the shutdown in parallel with the other new systems being bought on line.

Rockwell Automation was assigned as EPC contractor with responsibilities for placing orders with all equipment vendors, completion of all detailed engineering, organising control and shipment of all materials to site, supervision of vendor site installation and commissioning activities and management of the sub-contractors. The ESD and F&G systems were upgraded with a single Trusted triple modular redundant (TMR) ESD controller and a single Trusted TMR F&G controller.

Trusted is a fault-tolerant control and safety system, designed to meet the most stringent international safety standards, helping towards the integrity of a control system that could – if it failed – compromise process profitability. It has triplicated processing paths within each module, along with high levels of diagnostics and voting between the paths.

Unlike non-TMR control systems, Trusted is said to give virtually 100% uptime, without compromise to the safety integrity of the system. It is also approved to TUV AK6, for programmable safety systems and carries approvals for NFPA72 and Gosstandart of Russia.

The existing system employed by TOTAL E&P UK comprised an ICS 2000 safety system from Rockwell Automation. The Dunbar system Upgrade (DSU) replaced the processor and output sub-system with the Trusted processors and engineers were also able to do controlled online migration of the upgrade because of a great deal of pre-planning and risk assessment.

The project required the removal of one half of the old dual ICS2000 and constructing the new trusted into the same footprint. The input subsystem then needed to be configured so the input data was available on both the old and new systems concurrently to allow engineers to verify the processing logic and output states before transferring outputs to the new system. There was then a controlled migration of the outputs from the old to the new.
"One of the most important aspects from TOTAL's perspective was safety," said Derek Thomson, E&I projects manager, TOTAL E&P: "We base many of our operational statistics on safety and I am pleased to say that this project was exceptional in these terms. The engineers from Rockwell Automation arrived on the platform and integrated into a safety culture right away."

Remote control potential
One potential feature of the new installation will be the ability to control elements of Dunbar from Alwyn. The legacy system was designed to incorporate this feature, but it was never used. However it is envisioned that it may be put to use in the future. "The primary drive was down to reliability,” said Thomson. "We are now into phase two of the upgrade project, reinforcing the strong bond we have with Rockwell."

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