Ormen Lange Pipelines - Geotechnical challenges

The selected development scenario for the Ormen Lange gas field is a subsea tie-back to an onshore terminal located at Nyhamna in Mid-Norway. There are large variations in soil conditions along the 120 km long pipeline routes from shore to the template area. In narrow valleys in the near shore area one of the main challenges was to find enough space for installing all pipelines within the same corridor. The severe seabed requires rock supports for free span mitigation of the gas pipelines both near shore and in the deep water area. For the service lines, protection against trawling and dropped objects was required along the entire length and this turned out to be particularly challenging at the steep Storegga slide slope and in the rough terrain at the deep water area with soil shear strength of 1 kPa. The quasistatic stability of rock supports higher than 0.5 m was not satisfactory for the 10(-2) earth quake load event due to the soft soil conditions. A deformation criterion was therefore applied both for the 10(-2) and 10(-4) earth quake load events.