TURBOMACHINERY FOR ARCTIC FLOATING UNITS

As much as 30% of the world’s undiscovered natural gas and 12% of its undiscovered oil is estimated to be in the Arctic. Some of these reserves had previously been considered commercially unprofitable using older technology and based on relatively low prices of energy. But there have been efforts towards the development of technology for safe and sustainable operations in this polar region.

The Arctic is one of the most hostile working environments in existence, with prolonged darkness, snow precipitation, freezing temperatures, sea ice, and icing from sea spray. Temperatures can drop to -70°C, and there are strong winds and huge waves. The operational capabilities of traditional vessels, offshore systems and conventional machinery do not meet these requirements. A major issue, then, is a need for regulations and guidelines on the design and winterization of Arctic vessels, offshore structures and turbomachinery.

Both fixed and moored floating structures have been used in Arctic regions. Moored floating structures, employed for oil field developments and production in northern Canada, are important for future Arctic oil and gas exploration and production activities. It is necessary, therefore, to be able to predict and mitigate marine icing of Arctic floating units. In addition, machinery innovation suitable for floating units is vitally necessary.

Floating units present design and operating challenges over those associated with fixed offshore structures, due to their dynamic response under complicated ice-structure interaction processes. Load changes occur due to the impact from different sizes of ice (including ice ridges and icebergs), as well as the response of the vessel or structure. Incoming sea ice forms in different ways depending on structural configuration. Ice loads can be substantial. In many ways, it is similar to a conventional vessel battling the extreme forces of a hurricane.

Next generation offshore vessels are required for oil & gas production in heavy ice and harsh Arctic environments. Such a floating unit requires high-reliability operation. To counter the effects of Arctic sea ice, a well-designed floating unit is superior to other offshore options. The columns and sections found on platforms or semi-submersible units attract ice loading and can become locked in ice. However, a good floating design can offer more deck load capacity than other offshore solutions. This could be looked upon as a customized floating production storage offloading (FPSO) vessel with much better protection and covering.

Arctic vessels should be largely autonomous and capable of moving under their own power. They should also operate with higher thrust and loads, and travel faster than conventional production vessels. Such vessels must be supported by the right turbomachinery. Steam turbines are a good candidate for pumps and compressor drives. Steam generation boiler systems and steam turbine drivers have already been developed for offshore floating applications such as LNG carriers. And large submarines have experience using steam drivers in Arctic conditions.

Available technologies, then, can be deployed in Arctic production vessels. The immediate availability of cooling water can achieve relatively high efficiency for steam cycles. Additionally, steam turbines are compact and lightweight. While gas turbines are efficient, inlet air could be affected by extreme weather condition.

Perhaps an electric drive might be feasible. However, an all-electric solution using large generators, transformers and variable speed drive systems plus related facilities and auxiliaries could be too big and too heavy for a floating unit. But some element of electric power generation using steam turbine-driven generators would be required for any such unit. The best approach may well be the development of a dual- or multi-fuel steam generation system that can also be used to move compact and powerful steam drivers for vessel propulsion. During production time, the steam system can be used to drive pumps and compressors using compact variable-speed direct-drive steam turbines.