An innovation in deep water pipelines promises to cut the cost of bringing gas to shore across long distances.
Oil recovery is increasingly carried out in deeper water, further from shore, making the piping of by-product gas more difficult. To withstand the pressure of water at depths of 2–3000 meters, steel pipes must be extra thick, which reduces the diameter available for gas flow.
The sheer quantity of steel required makes these pipes so heavy that handling and installation requires specialised equipment. Only a few pipe mills worldwide are able to produce pipes at the necessary thickness, which also adds to costs.
The new concept, dubbed X-Stream, uses a system of valves to keep the pressure of the gas on the inside of the pipes equal to that of the water on the outside. As pipe collapse is prevented by pressure, the steel casing of the pipe can be thinner.
The valves are positioned on the oil platform, seabed and shore. Asle Vanås, global pipeline director of DNV, the company behind the project, said: “By utilising an inverted high pressure protection system and inverted double block and bleed valves the system immediately and effectively isolated the deep-water pipe if the pressure starts to fall. In this way, the internal pipeline pressure is maintained above a critical level for any length of time.”
Estimates suggest that the system reduces the thickness of pipe casing by a third. The casing for an 18inch diameter pipe falls from 25mm to 15mm with the valves in place.
Vanås added: “Reducing the wall thickness will enable an increased diameter for gas flow and will give savings in steel and installation. It will also decrease welding times.”
Further reductions in steel thickness are possible but the pipe then becomes too light, he explained. Adding concrete to the outside of the pipe to counter this makes reductions of up to 37% possible.
DNV's calculations suggest that the use of the system could shave 1billion Euro off the 15.5billion Euro south stream project – a proposed deep sea pipe linking gas from Russia to Bulgaria, Greece and Italy via the Black Sea. Other areas that could reap the benefits of the technology include the Oman to India deep-water gas line, as well as developments in West Africa, West Australia and the Gulf of Mexico.
The idea was developed by a team of young DNV engineers based in Brazil. The 10-strong team with expertise in maritime operations, pipelines and safety came up with the idea in two months. Dr Henrick Madsen, chief executive of DNV, added: “We had to use the young engineers because the older ones get caught up with the way things are done now.”
The group discussed several options, including floating pipelines, before developing the X-Stream system.