Rory MacKenzie
Total SA
To address the future subsea development challenges of remoteness, environmental requirement, and reliability, the oil and gas industry needs to explore new technological avenues. For instance, all-electric control systems are believed to be one of the major technological steps that will help create new opportunities.
Total addresses these challenges through strategic technology development and qualification projects. A case in point is the K5F project which piloted the first all-electric tree and control system in the Dutch North Sea. All-electric technology paves the way for more complex subsea processing systems and, coupled with fiber-optic (FO) communications, enables ultra long tiebacks. This is further confirmed by the Laggan/Tormore project, a 157 km (98 mi) subsea to beach tieback in the west Shetlands area of the North Atlantic. This project incorporates FO communications and potential future addition of wet gas compression.
Total also focuses on development of subsea control system infrastructure. Adopting FO open architecture control system designs as a base case on all current and future projects prepares these developments for future technology integration and field extensions. Proving the core technologies necessary for seabed-wide communication and control infrastructure that is neither constrained by, nor impacts the performance of the wellhead control system is a significant step.
The ability to communicate to any subsea device on an industry standard TCP/IP protocol enables future integration of complex sub-systems such as subsea processing, gas compression, reservoir monitoring, etc. It also faces the growing need to address obsolescence and advanced system condition monitoring. The use of standard interfaces and communication protocols also allows upgrades, replacement technology, and extended functionality to be introduced at a sub-system level without impact on the core control system.
The extension of surface network techniques to subsea systems brings many tried and tested tools to the operator such as bandwidth allocation, message prioritization, network storm protection, and diagnostics through simple network management protocol (SNMP).
Short-term benefits of a high bandwidth open architecture also are significant. Most importantly we can remove the burden of data acquisition, validation, routing, and transmission from the subsea production control system (PCS) processor to an intelligent network management device. These devices are well established on surface systems and provide a level of flexibility and functionality unavailable subsea.
The following list highlights some of the more pertinent characteristics:
Plug and play.Open architecture reduces interface development and testing costs and allows new sensors to be added as they become available with limited integration requirement
Transparent connectivity.The open network allows surface acquisition systems to communicate directly with the sensor on the seabed or downhole. This means communication handshakes between the two devices is direct rather than to the PCS processor on the surface and subsea, providing autonomy with respect to functionality and future software upgrades; it also reduces the overall workload on the PCS
Expandability.The open network permits electrical and mechanical interfaces to be pre-installed for future sensor installations. This facilitates the procurement of the subsea monitoring and control equipment without the need for upfront information about the final sensor requirements and interfaces. The ability to route serial communications over the network allows sensors to be interfaced easily after installation of the surveillance system with the provision of mechanical interfaces and subsea wet-mate connectors
High bandwidth.Advanced surveillance systems link communication with bandwidths in the region of GB/sec. This high-speed link allows real-time data, including diagnostic data, to be acquired from existing subsea sensors and also enables the use of new sensors and data rate intensive equipment such as subsea video, leak detection, downhole seismic, and inspection and maintenance/repair support.
Based on these concepts, Total has updated its general specification for subsea production control systems. The key aspects are:
- Topside control equipment is developed from industrial PLCs and or DCS controllers
- Elements integrated in ICSS network are developed with ICSS vendor components
- Each subsea loop shall comprise of independent A and B control from SCU to SCM
- Subsea communication shall be high speed FO using an industry standard TCP/IP protocol
- Local subsea network from SRMs is electrical using industry standard TCP/IP protocols
- Subsea power distribution is switchable at SRMs
- Third-party equipment has direct router access topside and subsea (SCM and SRM)
- Spare Ethernet connections available at SCMs and SRM
- 100% spare FO capacity available at each manifold.
The flexibility of this architecture prepares for future complexities when implementing more advanced subsea systems. One example is that of subsea gas compression (SSGC). An SSGC system will have to incorporate multiple vendor control systems, unique condition monitoring sub systems, shutdown and equipment integrity, closed-loop control systems, and all the standard subsea systems such as manifold valving, power distribution, and chemical management.
Another consideration with respect to life of field operability is obsolescence issues as we attempt to upgrade aging infrastructure or repair failure of aging equipment, materials, and software. In the case of the subsea control system, this is particularly critical as many of the internal electronic components can be obsolete by the supplying manufacturer within only a few years. This means a strong emphasis on modularity, ease of modification, and reparability must be prioritized during design.
Operational experiences with Total's assets highlight this issue. For some years this issue has been magnified in West Africa due to the remoteness from main manufacturing centers for subsea control systems. This, coupled with a growing concern about our ability to efficiently maintain subsea equipment throughout the life of field, is the subject of numerous studies within Total over the past few years. Component obsolescence is intrinsic to all commercial products.
Component life cycles are subjects of many factors: market life cycles, component production costs and volumes, the technologies used, and the number of competitors. The main causes of obsolescence typically are:
- Technology advances, this makes innovation cycles shorter: new technologies replace older ones which in turn become obsolete
- The original manufacturer goes out of business or the original supplier decides to stop manufacture
- The product is no longer viable to produce.
Our industry has no influence over any of these factors and must, therefore, accept component obsolescence as a fact of life. Rather than looking for a cure we must instead learn to manage it. By learning from other industries such as defense, nuclear and the aeronautical industry, and tapping into already mature processes from these industries Total has produced a general specification that requires a proactive obsolescence management system to be in place for all our subsea suppliers.
The IEC 62402 standard has been used as the baseline for the Total general specification on obsolescence management. The specification defines minimum requirements in terms of design, component monitoring, and creating adequate reporting systems back to Total to permit proactive action. A basic aim of the proactive obsolescence management system is to extend choice in terms of the obsolescence solutions away from costly redesign.
The remaining issue is industry acceptance. Other operators also are developing processes to manage this issue. It is important that suppliers do not end up with widely different requirements from its customers. A number of initiatives are starting to appear on a joint-industry basis and this is strongly encouraged. It is our hope that over the next few years an industry standard obsolescence management endorsed by all operators system can be developed.
The focus on efficient project management and successful application of innovative technology has never been greater. With more than 80% of its producing subsea wells in deepwater, Total has had to embrace novel installation techniques, push existing technology to new boundaries, and pioneer advanced development methodology. The high success rate of these developments is not by chance, it is built on experience, highly developed processes, and vigorous qualification programs. It is in this vane that Total strives to optimize its technology readiness for future subsea challenges. The open architecture control system infrastructure together with effective obsolescence management will contribute significantly toward this aim.
