Detailed Description :

The Thames Complex processes and transports production from:

• Thames platform wells (5 off)
• Yare & Bure subsea wells
• Welland and Tristan wells via Welland satellite platform
• Orwell satellite subsea wells
• Gawain satellite subsea wells (subject of a separate project)

Remote operation of the Thames Complex was implemented in Spring 1995 when existing compression facilities were updated and a third Thames compressor serving the Orwell Field was installed, commissioned and operating in a trouble-free manner.

This is the first time that a North Sea offshore installation with gas compression facilities is operable by remote control from onshore.

The target attendance is for operators and maintenance staff to attend offshore for three days every week (staying offshore overnight). However, there are operational advantages in adopting an offshore rota of a week on/week off on Thames if this can be achieved. In addition, unplanned visits are anticipated approximately once every two weeks.

Operators and maintenance technicians will be based onshore at Great Yarmouth when not on Thames.

Planned visits to the Complex shall be primarily to carry out maintenance activities, but the maintenance crew will also be capable of carrying out operator interventions and checks. The maintenance crew will also be capable of assuming local offshore control if necessary, although normal control will remain with the Great Yarmouth Control Room even when Thames is manned.

Well tests of Thames/Wensum/Yare/Bure and Orwell wells will only be carried out during planned maintenance visits.

A new Thames Process Control System (PCS) supplied by Fisher Rosemount has been installed in the Great Yarmouth Control Room, currently used to control the two Pickerill satellite platforms. The new system will monitor and control all Thames Complex equipment, and will interface with the existing Welland (ICS Bailey) and Orwell (FSSL) Control Systems, as well as the Thames Emergency Shutdown, Fire and Gas, Metering and Compressor Control Systems. The PCS is duplicated in the Thames Control Room, to allow Operator control facilities from either onshore or offshore.

PCS remote restarts and resets are provided for process and utility equipment and valves for emergency (process) shutdown of levels 1 and 2. Levels 3 and 4 will require a platform visit however. Fuel gas trips of Level 2 will also require a platform visit.

A new PLC (Programmable Logic Controller) based ESD system has also been installed as part of the Optimisation Project. The system being supplied by Skil Controls/Silvertech replaces the original relay based system and comprises new equipment frames installed within the carcass of the existing panel.

The ESD System Interface with the Fire and Gas System allows remote indication and monitoring of the system at the Great Yarmouth Control Room. The status of fire pumps, vent snuff and the extinguishant release is also provided at Great Yarmouth, together with the facility to manually initiate these systems.

Compression facilities comprise two existing RB8 single stage compressors driven by Ruston TB5000 turbines which can be configured in parallel or in series. They are currently operating in series mode compressing Thames production only. However, they can be operated in parallel or series mode depending on field nomination requirements. The third compressor was supplied by Mannasmann Demag ad driven by a Solar Mars T14000 turbine. Initially Thames production will be compressed in the compressor first stage and Thames and Orwell production in the second stage. The Demag compressor uses dry gas seals, whereas the Coopers compressors have a seal oil system.

As part of the Thames Complex Safety Case the recommendation was made for the process area of the AP platform be blown down first. This was not achievable with the existing Coopers compressor seal oil system and the decision was taken to install dry gas seals to the shafts of these units. This also necessitated modifications to the Thames Complex blowdown sequence by carrying out modifications to the Thames Complex blowdown sequence by carrying out modifications to the ESD system and the compressor controls logic.

Control and monitoring of all three compressors has been achieved by a serial link between their individual control system and the PCS.

Modifications to the metering system have included the automation of metering tube isolation valves which will enable additional tubes to be “brought on” as required. Transfer of metering allocation data to Great Yarmouth has been achieved by a PC to PC link with the Export Tracking Computer. Other modifications to the metering system include the replacement of 9 existing panel mounted stream computers.

The primary telecommunications link between the complex and Great Yarmouth is provided by a new Line of Site to the Phillips Control Room at Bacton (via Amaco 27A platform) and a megastream link between Bacton and ARCO’s Great Yarmouth Control Room. This system has a calculated availability of approximately 99.9%.

Modifications have been undertaken to the power generation system. These allow for remote operation of all generation facilities and load shedding from the Great Yarmouth Control Room. Additionally when the platform is left in an unmanned mode a facility has been provided whereby non essential electrical services can be isolated.

Various modifications have also been carried out on the utility systems i.e. MEG, TEG and Heating Medium. These enable the packages to be controlled and monitored by the PCS as opposed to operating in their original local mode.

Another first for this project has been the modification of all existing manual drawings using CAD facilities. This has been achieved by the provision of scanned drawings in datafiles which are then converted to enable modifications (to the scanned image) to be made in AUTOCAD 12.