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Control System Upgrades for Tordis and Vigdis Field - A Project Case Study of Revitalising Brownfield Developments with Next Generation Subsea Controls Karl Herman Frantzen, Engineering Manager - Statoil; Ian Kent, Chief Engineer, Subsea Controls & Informatics, and Ray Phillips, Product Marketing Manager - GE Oil & Gas

Copyright 2011, Offshore Technology Conference This paper was prepared for presentation at the Offshore Technology Conference held in Houston, Texas, USA, 25 May 2011. This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflect any position of the Offshore Technology Conference, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of OTC copyright.

Abstract Since the 1980s, multiplexed electro-hydraulic control systems have been successfully employed in subsea oil and gas production. With field lives extending, and the original equipment becoming more difficult to maintain, particularly because of electronic component obsolescence, it is possible by applying new generations of control system equipment to bring enhanced controls capabilities into brownfield developments. From the inception of the Tordis/Vigdis Controls upgrade & Modification programme (TVCM), it was seen that a number of the design limitations of the legacy system could be overcome when upgrading to a modern and flexible communications system with standard comms interfaces. There were some specific limitations of the installed system, and in addition, for the legacy system, electronic component obsolescence was becoming an increasing burden in support of continuing production. Following the completion of the upgrade under the TVCM programme, the new system will deliver significant step-changes in the performance envelope of the overall Control and Instrumentation System, including improved reliability, a new configuration employing Open communications protocols between topsides and subsea with the communications bandwidth available to the Tordis producer wells upgraded to 1Mbit/s. A novel feature, and a key success factor for the project, is the use of Subsea Control Module interface adapters. Background The Tordis and Vigdis oil fields lie in block 34/7 in the Tampen area of the Norwegian North Sea, and came on stream in 1994 and 1997 respectively, developed with subsea installations and operating in water depths from 200m to 280m. In addition to the main Tordis structure, the development embraces the Tordis East (1998), and Tordis South East (2001) fields.

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Figure 1 Layout of the Tordis and Vigdis Fields For the Tordis field water injection is used to maintain pressure in the reservoirs, and the well stream from Tordis is routed through two pipelines to the Gullfaks C platform 10km away for processing, storage and export. Vigdis has been developed with subsea installations tied back to the Snorre A platform 7km away for processing. Gas separated from the main Vigdis structure is injected into the Snorre field, while gas from Borg North-West and Vigdis East is piped from Snorre A to Statfjord A. The former Saga Petroleum company became operator for licence PL 089 when the licence was awarded in 1984; subsequently Norsk Hydro took over operatorship after acquiring Saga in 1999, with the operatorship passing to Statoil on 1 January 2003. Limits and issues with current system

From the inception of the Tordis/Vigdis Controls upgrade & Modification programme (TVCM), it was seen that a number of the design limitations of the legacy system could be overcome when upgrading to a modern and flexible communications system with open standard comms interfaces. Early 1990s control and communications technologies were to be replaced with 5th generation subsea controls and communications technology. (Multiplexed electro-hydraulic control of subsea wells began in the early 1980s and has evolved through subsequent generations of equipment, with 5th generation equipment design for introduction from 2010.)

Some of the specific limitations of the installed system were seen as:

The existing system delivered low bandwidth communications from subsea-to-surface (a communications bit rate of 1.2 Kbits/sec).

The existing Subsea Control Modules (SCM) did not meet todays expectations and the updated standards of ISO 13628 Pt 6.

Different parts of the Tordis and Vigdis fields had non-interchangeable subsea control modules from two different vendors.

In addition, for the legacy system, electronic-component obsolescence was becoming an increasing burden in support of

continuing production, and the sensor set fitted to the Trees and Manifolds was limited to basic pressure and temperature sensors.

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It was anticipated that, following the completion of the upgrade under the TVCM programme, the new system would deliver significant step-changes in the performance envelope of the overall Control & Instrumentation System, viz:

Improved reliability of the subsea control system. The new configuration would embody Open communications protocols between topsides and subsea. The Communications bandwidth available to the Tordis producer trees should be a minimum of 1 Mbit/s. Additional instruments incorporated to enhance surveillance of the infrastructure.

Requirements/expectations All of the system requirements and expectations for the TVCM programme were taken as the Basis of Design for a field

upgrade FEED study, and the optimal solutions from the study were adopted into a Functional Design Requirements (FDR) specification. Some of the key elements of the FDR were as follows:

The upgrade is to achieve an improvement in system availability as a contribution towards the IOR (Improved Oil recovery) ambition of Statoil. The target system availability to be better than 99%.

The system design should, wherever possible, be future-proofed to allow extended field-life out towards 2030/2040.

The upgrade should take advantage of all opportunities to reduce the exposure to component obsolescence (particularly for the electronic components).

The upgraded system is required to provide a step-change in subsea-to-surface data bandwidth, to accommodate a range of more sophisticated subsea sensors and allow the potential for system growth in the future.

The upgrade is an opportunity to incorporate SIIS (Subsea Instrument Interface Standardisation) and IWIS (Intelligent Well Interface Standardisation) Standards compatibility for sensor interfaces, and in the provision of spare interfaces for any sensors added in the future.

The upgrade would allow the inclusion of additional downhole, high-pressure control line functions to be included in the Subsea Control Module the field development team wished to have the future option to re-complete the wells using intelligent well completions.

A parallel approach to installation of the upgraded system should be taken, with most wells continuing to operate, to minimise disruption to hydro-carbon production as we migrate from the old system to the upgraded system.

The introduction of standardised equipment should provide an opportunity to share capital equipment and component spares across different subsea assets.

In conjunction with the above system-wide expectations, the opportunity arose for some detailed improvements on the previous design, such as incorporation of hydraulic isolation valves in the subsea hydraulics distribution network, and the introduction of remote electrical power switching capability into the subsea communications and power distribution hub at the manifolds. Finally the upgrade would also facilitate the change to a water-based, environmentally-compatible control fluid.

Challenges Since the requirements and expectation of the field Operator, Statoil, were to be applied to an existing operating field, it

was necessary to recognise the challenges for a new design when fitting into the existing field infrastructure. One of the primary challenges was that no new umbilicals were to be deployed however it was possible to make use of

the existing Tordis SSBI (Subsea Separation, Boosting & Injection System) umbilical which had spare fibre optic links already incorporated.

Some other specific challenges were:

The original equipment fit had a common tree design across the Tordis and Vigdis fields but the control modules were legacy equipment from two different vendors.

The trees were to be left in place and not recovered to the surface - hence legacy tree sensors must interface to the new control system.

Field down-time, while implementing the controls upgrade, had to be minimized. The uncertain status of the installed equipment and structures ROV surveys were needed to establish the precise

configuration, and extensive simulation of ROV-intervention operations was carried out to establish that the ROV would have a practical and safe operating envelope.

The two separate controls centres for the Tordis and Vigdis fields were to be maintained (Tordis controlled from Gullfaks C with an ABB SAS System and Vigdis controlled from Snorre using a Siemens SAS System) while equipping the two subsea systems with common subsea equipment.

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Early recognition of the challenge to achieve safe, parallel operations for the changeover process from the existing control system to the new one requires identification of all the stakeholders who need to be involved in a detailed HAZOPS/HAZIDS process, and confirmation that the new design delivers features to achieve the safe and efficient changeover.

Technical Solutions

Figure 2 VetcoGray SemStar5 Subsea Electronics Module SEM With the introduction of a 5th generation subsea electronics module satisfying the project requirements for future-proofing the field and mitigating component obsolescence, a number of other specific technical challenges required resolution to complete the project portfolio, and some of these are highlighted below. Subsea Control Module Adapter Plate

Figure 3 SCM Adapter Plate As identified above, a requirement for the project was to replace subsea control modules delivered by two control system

suppliers with a new common subsea control module. Both of the existing systems reflected their companys designs from the original delivery periods, and neither was compatible with the current GE Oil & Gas Subsea Control Module design the VetcoGray ModPod.

The solution to this technical challenge was achieved through the use of Adapter Plates. These are units which are fitted to

the bottom of a subsea control module prior to deployment, which adapt its functionality to the tree onto which it is being

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installed, in terms of physical fit, hydraulic connections and electrical connections, and take account of height and other space limitations imposed by the tree structure.

Subsea Electrical & Communication Distribution System The subsea power and communications distribution system design is a key factor in realising Statoils requirements for the

TVCM development. The system is designed as a point-to-point topology from topsides facilities to distribution modules, and then a star network out from each distribution module to the subsea control modules located on the trees and manifolds.

The base case of the revised communications system for Tordis was to include fibre-optic communications from the

topsides facilities down to the distribution unit, with backup powerline communications. The on-template distribution has been realised using a copper-based connection system, running at 1Mbit a simpler system than fibre-optic connections, but able to deliver a relatively high bandwidth connection.

The subsea Power Communications Distribution Modules (PCDM) are units which are located on the manifolds on

TVCM to provide an infrastructure for distributing both power and communications to the subsea control system. To maximise system availability, for each system, two PCDMs are deployed, each one controlling one of the two subsea

control system power and communications channels. The new distribution system, selected after a thorough Reliability/Availability/Maintainability (RAM) comparability analysis, is a major contribution to the improved availability of the control and instrumentation system.

Figure 4 Dual Channel Power & Communications; re-routed Communications following loss of one fibre channel

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By using common system components for the Tordis and Vigdis upgrades an option has been provided to allow upgrade of the Vigdis system to fibre-optic communications when the umbilical is upgraded in the future, with the use of a common PCDM between fields.

System features provided by the PCDMs include:

Remote power control and protection are provided within each PCDM. Each power output from the PCDM can be controlled individually from the surface, allowing the SEMs within the subsea control system to be isolated.

Communications media conversion The PCDM acts as a media converter between the point-to-point primary (fibre-optic) or backup (power-line) comms system, and the infield comms system.

Back-up comms As mentioned above, on Tordis the primary comms system between the topsides facilities and the PCDM utilises a 1-Gigabit fibre-optic link. To maximise system availability, a backup communication system is available on each PCDM using powerline communications.

The patented TCP/IP routers implemented within the PCDMs maximise the use of available communications within the system. If one fibre channel is lost, the routers may automatically route the data to the remaining fibre, thus requiring both fibres to be lost before switching to powerline communications. If both fibres are lost, the system will automatically switch to the back-up powerline communications.

Subsea Control Module Instrumentation Interfaces The upgraded control system for TVCM is designed to integrate with open architecture instrumentation using standards

such as SIIS and IWIS, however for this project an additional requirement was to interface to older, legacy instruments which have been fitted to the trees since installation.

Legacy Instrumentation This technical challenge was managed through the implementation of a specific SemStar5 support module which provides

an interface to two quartz frequency pressure and temperature sensors, and two RS232 serial input intrusive sand detectors. Now designated the legacy instrumentation support module (LISM) the new design was verified using both simulators of the older instruments, and spare physical instruments.

Open Standard Instrumentation A number of new instruments have been included which utilise the open architecture protocols. These include:

SIIS Level 2 Capacitance Hydrocarbon Leak Detector located on Tree. SIIS Level 2 Acoustic Sand Detector. SIIS Level 3 Acoustic Hydrocarbon Detector located on the Manifold. IWIS Physical Option 3 Module located on Tree.

The SIIS Level 2 instruments utilise fault-tolerant CANopen for communications with the SCM. In normal operation the

data from these devices is embedded in the production control system data. For maintenance purposes, a transparent link may be instituted in accordance with CIA-309:3.

The SIIS Level 3 instruments interface with the subsea control module is provided via a 10Mbit TCP/IP communications

link. The data-flow from the instrument to its topsides interrogation system is provided transparently through the control system via the subsea network.

The IWIS interface is provided through the use of an external IWIS canister in accordance with IWIS Physical Option 3 as

defined by ISO13628-6. A redundant comms interface back to the control module allows either SEM in the control module to communicate with the interface card. The use of external IWIS modules allows a standard control module to be utilised where different wells may have different downhole equipment suppliers historically three different downhole gauges had been fitted to the wells. By contrast IWIS Option 1 solution, where the interface card is hosted within the SEM would result in different SCM build standards. Through the use of IWIS and its transparent topside-to-subsea interface, the subsea control system has no requirement to know which type of intelligent well interface card is utilised on any well.

Topsides Integration As both the Tordis and Vigdis fields are connected to different topsides facilities, the topsides controls systems on each

were supplied by different SCADA/SAS system suppliers, ABB on Tordis and Siemens on Vigdis. To maintain a standard component approach, the Subsea Power and Communications Unit (SPCU) contains a common engineering station for both fields, and common interfaces out to both SCADA systems.

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The changes to the existing screen displays have been kept to a minimum by only adding presentation of the newly-installed instruments. Thereby, the control room operators interfaces will be as before, with only a minimum of changes. This will reduce any operating risks associated with changeover and avoids special training requirements.

The new system offers an extensive array of diagnostics and housekeeping information. Most of this is kept within the SPCU and can be accessed via the Engineering Workstation on the platform, from Statoils technical network, or from the vendors SmartCenter.

Remote Monitoring & Diagnostics for the Umbilical

A new method of accurately measuring umbilical Line Insulation breakdown is implemented in the Umbilical Monitor Device (UMD). These units are integrated into the SPCUs and will provide real time trending of umbilical isolation characteristics.

Single-Pressure Hydraulic Supplies

The Subsea Control Modules receive redundant low pressure hydraulics supplies at 207bar from the surface, and internally generate high pressure hydraulics supply for downhole functions at 517bar by using High Pressure Intensifiers within the SCM.

SCM Standardization

Two variants of SCM have been produced to fulfil all the TVCM requirements. One variant used for manifold applications, which has fewer hydraulic functions and lesser instrumentation, and a single variant which can be used for all Tree applications (both Production and Injection) across both fields. Configuration for operation between the differing installation scenarios requires only a configuration file to be loaded into the SEMs.

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Control Module Installation/Retrieval

Figure 5 Tree & Control Module Integration Testing using the RCR Running Tool The RCR (Remote Component Replacement) tool is designed to install and retrieve the Tordis/Vigdis SCMs both with and

without mounting base adapters fitted. The tool has its own dedicated transport skid and component loading skid which allow lifting of SCMs onto the installation

vessel and to facilitate handling on deck. RCR is designed to be deployed at 5.5m sea state through the vessel moonpool with all of its hydraulic functions operated by an ROV. Functionality of the RCR is sufficient to provide all the necessary actions to install/retrieve the SCM without need of any additional tool during normal operation. Features include a guidance system, an internal depressor beam used for final mating, and built in torque tools to lock and release the control module to/from the subsea structure.

The RCR interfaces have been confirmed through 3D model checks, ROV simulations and though Site Integration Testing

(SIT).

Maintaining legacy functionality In the original design of subsea control system, the SCMs played an active part in the distribution of injected chemicals

with these (diesel fuel and methanol) brought into the control system for injection into the process flow. This injection system

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has been replicated in the replacement TVCM subsea control modules through the inclusion of hydraulically-piloted diesel/methanol valves and pressure sensors on a chemical line routed through the SCM. In summary, the solution derived represents a significant, step-change in technology to extend the operational life of the Tordis and Vigdis fields by introducing a highly available and modular system with built in redundancy/failure survival features. The introduction of optical fibre based, point-to-point communications links to the Tordis field, with in-field distribution of high bandwidth communications, provides a minimum of one 1Mbps communications bandwidth per SEM, whilst enhancing the redundancy available to the operator through the use of dynamic subsea routing. Experiences As Subsea has become a mature field development strategy, more of the earlier fields with subsea facilities are becoming candidates for brownfield upgrades so experiences/lessons learned may be of particular interest across the industry. The TVCM project began its Concept Appraisal Cycle cycle in 2007, with the FEED Definition Study executed in Q3 of 2008. Project execution began in 2009 with a significant offshore installation campaign planned for later in 2011. The project is run in two phases. Tordis is first, having an EFAT (Extended Factory Acceptance Testing) early 2011 and equipment to be installed mid-2011. Vigdis will follow closely after and is planned for installation late 2011/early 2012. Some of the lessons learned to date are described below. The novel feature for this development has been the use of subsea control module interface adapters. The use of Adapter Plates is a key success factor for the project, and due to the risks associated with that, a very detailed engineering and analysis exercise was performed during the FEED phase. Thanks to this, the implementation of this solution has been very smooth, with a comprehensive qualification programme carried out to demonstrate the functionality. The Adapter Plates are now ready for deployment together with the SCMs. A brownfield project like this has a large number of stake holders and a corresponding large number of interfaces. It has been a challenge to define and completely align all parties expectations and requirements solely on the basis of technical standards and contractual documents (scope of work and scope of supply). The execution of the TVCM project has drawn significant benefit from continuity of technical staff from the FEED work through into project execution. This has necessarily involved close collaboration between vendor, other contractors and the Operator company. The project team has also had a high focus on keeping all interested parties up-to-date and involved in the project. The project execution has demonstrated that fitting new equipment to an existing infrastructure which has been subsea for a number of years is very demanding and complex. The non-availability of 3D CAD models and the historic use of different tolerance criteria are just two examples requiring some focused work-around time. Significant efforts have been required to verify that available documents reflect the current state of the equipment. Thanks to a very comprehensive and up-to-date electronic documentation system all key engineering documents were made available. The process of updating all documents affected by the changes is another area which has proven to be large and demanding. While we have confirmed the value of time spent on integration and commissioning of the real system this uncovers interactions not identified in acceptance testing of the separate system components it should be emphasised that thorough methodologies for environmental qualification and performance-envelope confirmation are a necessary precursor to successful integration. This, combined with a slow, systematic build-up (block by block) of the complete system, has lead to smooth initial hook-up for EFAT and Site Integration Tests.

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Figure 6 SCM under test with integrated Adapter Plate For the vendor, this brownfield project has involved different ways to operate than for a greenfield EPC contract. A much closer collaboration than usual has been required between the aftermarket departments and the product engineering team. Also on the system side a critical and demanding process has been undertaken in order to assure a smooth changeover of a live plant. As a result of collaborative efforts the interface of the SAS to the topsides-located SPCUs has been a very smooth process. The history of these two fields, through changes in operator and with subsea facilities from several vendors, showed the value of tracking down the legacy installed configuration using ROV surveys and ROV simulations to properly bottom out the exact installed connectivity and layout.

Figure 7 ROV Survey of the Tordis Manifold (Image courtesy of Acergy and Statoil)

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Figure 8 Typical ROV Intervention Simulation (Image courtesy of Oceaneering) At the time of writing (January 2011), the offshore installation campaign for the Tordis field has started, with some equipment already installed. The first installation campaigns have laid out all overtrawl-protected, electrical cables between structures, and pulled the connectors into parking positions inside the existing structures. Installation baskets for new equipment like the PCDM and DHPT (Downhole Pressure and Temperature) interface canisters have also been installed. The critical parts which demand fitting to existing structures are now mostly in place for Tordis, proving that retrofit installation of the additional equipment is possible. The equipment has been designed for installation at high sea states. This has allowed installation campaigns to be carried out through the winter time, without excessive standby time. An EFAT is underway. This is primarily to verify that all parts of the system work well together. Every well operation will be tested, under very realistic conditions. The EFAT also provides opportunities for operator training and familiarisation for the field-service engineering team. As soon as EFAT testing is finished, topside equipment will be installed on Gullfaks C and the installation of the remainder of the subsea equipment can start. The installation/commissioning phase is planned to be done by only shutting-in one well at a time while keeping the shutdown time to a minimum. A detailed and comprehensive changeover and commissioning plan will be executed. The project ambition is to complete the installation and commissioning of all 27 new control modules with associated new equipment by early 2012.

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