The Oil and Gas industry, particularly in the North Sea and the Norwegian Sector, has been pioneering innovative concepts and technologies since day one.
Given the current focus on the environmental impact of the energy sector there is a greater need than ever to push boundaries. Whilst certainly not breaking news, the concept continues to make headlines, not just for new field developments, but in retrofitting existing offshore facilities.
Offshore carbon footprint
Offshore oil and gas facilities are very large consumers of power and declining field pressures and the drive for enhanced production only increase the energy demand through the life of a field. The power demand of a single platform can easily exceed 100 megawatts, in the main generated by gas turbines fuelled by the gas produced. Because the turbines are sized to meet peak demands they typically operate at reduced load conditions and therefore low fuel efficiency. The result is that the energy efficiency and reliability of these turbines is poor compared with typical onshore, grid-supplied electrical power generation. Offshore gas turbines are also costly to operate and maintain and take up significant real estate on board an already space-congested facility. Increasingly concerning for operators, and the main driver for power from shore, is the fact that offshore power generation by gas turbines produces a very large carbon footprint.
On the Norwegian Continental Shelf (NCS), for example, oil and gas installations emit approximately 13 million tonnes of C02 equivalents per year. Over 160 gas turbines account for 84.6% of the total C02 emissions from the NCS and roughly 30% of Norway’s total greenhouse gas emissions. It is no surprise, therefore, that Norwegian Operators, Equinor and Aker BP are leading the way when it comes to embracing power from shore.
Reliable and eco-friendly
The benefits are more than just environmental: although there are potentially higher costs from connecting the platform to shore, this is offset by lower operating costs due to the greater efficiency of shore-based power generation. For new facilities there is also the potential benefit of a smaller offshore footprint. Power from shore has a further advantage in being a more secure and reliable power supply, as well as being eco-friendly. In Norway about 99% of electricity generation comes from reliable renewable sources such as hydro and wind.
Troll A, was the first offshore platform to be powered from shore. Unusually, given that Troll A began operating in 1996, it was never intended to generate its own power but designed instead to receive electrical power from shore. Although sufficient when launched further power was later required to run an additional four gas export compressors; two in 2005 and a further two in 2013. These required four new power cables from shore and power conversion equipment delivered in two projects. The system uses HVDC (high voltage direct current) technology which takes AC (alternating current) from Norway’s national grid, converts it to DC (direct current) and transmits it to the platform via 70 km-long HVDC cables. At Troll A, the electrical power is converted back to AC to run the compressors.
HVDC vs HVAC
Other power from shore systems use HVAC cables. AC cables are a proven technology, but electrical resistance in AC cables increases with the length of the cable resulting in a reduced power supply. The power delivered by HVDC, on the other hand, while not compromised by distance, requires AC-DC conversion equipment both onshore and offshore which comes with its own costs both financially and in terms of physical space. Depending on the cable distance and power levels required this can be partly or even fully offset by the cost of the cables.
AC power from shore technology has been refined and is now successfully utilised on a number of offshore facilities, such as Gjøa and Goliath. Both developments comprise cables of over 100 km in overall length, achieved by transmitting power at very high voltages. The Gjøa and Goliat cables are also innovative as these facilities are floating production facilities, requiring the shore electrical power cables to comprise both static cable sections, which lie on the seabed, and dynamic sections which span the water column from the seabed to surface. The design of these dynamic cable sections is sophisticated and has to be sufficiently robust to withstand the loads and motions imposed on them as a result of marine and wave actions, much like dynamic production risers and control umbilicals. The intricate design and complicated processes involved in manufacturing the cables can also result in some interesting and significant problems, resulting in potentially costly insurance claims.
Onshore in action
The Martin Linge platform receives shore power via the world’s longest AC subsea cable measuring 162 km. Ormen Lange, Valhall and Johan Sverdrup fields are also powered directly from shore. Vega is also operated with power from shore via its host installation Gjøa, and Hod, via Valhall.
The Edvard Grieg, Ivar Aasen, Gina Krog, Solveig and Hanz fields will in due course receive power from shore via phase two of the Johan Sverdrup field development. The Duva and Nova fields will be operated with power from shore via Gjøa. Together these 16 powered from shore facilities will reduce Norway’s CO2 emissions by 3.2 million tonnes per year.
A further six power from shore projects have reached the advanced phases of planning: Troll B and C, for which contract award was announced on 15 January 2021, Oseberg Field Centre and Oseberg Sør, Sleipner and the Melkøya onshore facility. An investment decision was made for Sleipner in May 2020, and the project is now under regulatory review. The project will also provide power from shore to the associated fields Gudrun, Sigyn, Gugne and Utgard.
Perhaps the most innovative project is Equinor’s Hywind Tampen project which will see the Gullfaks and Snorre platforms provided with power from an 88 megawatt floating wind farm, comprising 11 turbines in 260 to 300 metre water depth. An investment decision was made in October 2019, and the project is expected to come onstream in late 2022.
Significant investment – significant emissions reduction
It is not just in the Norwegian sector where there will be further development in power from shore. In its recent energy integration review the UK’s Oil and Gas Authority identified the technology as a means to achieve significant emissions reductions towards a net zero target. Other energy integration technologies being considered to help deliver on this target include Carbon Capture and Storage (CCS) and blue and green hydrogen.
Power from shore represents not just a significant investment from the oil and gas industry but a major commitment by operators to reduce the environmental impact of both new and existing exploration and production facilities. It is another example of the oil and gas industry in transition, and we continue to keenly monitor developments in Norway, the UK and other regions that will inevitably follow suit.
Chris Brown
Managing Director – Natural Resources, UK, Europe and Singapore
chris.brown@charlestaylor.com
Expertise:
Loss Adjuster, Marine Engineer, Mechanical Engineer, Marine Surveyor, Natural Resources, Drilling & Production
Location:
London
