Offshore platform under rough conditions

The offshore platform Arkutun-Dagi, to be placed in 35 metres of water east of the Russian island Sakhalin in the Okhotsk Sea, will be exposed to extreme loads and weather conditions during its 40 years of production of oil and gas. NGI was responsible for the geotechnical design and the stability of the platform.

The humid and cold air in the Okhotsk Sea makes the climate tough for people, but for the Arkutun-Dagi platform, the conditions are even worse with heavy waves rolling on to the platform every day. In the winter, the sea freezes, which may lead to enormous loads when the ice starts drifting and forcing its way onto the platform. An even greater impact are the loads from severe earthquakes that may occur in the region.

Sakhalin-1 is a joint venture between the Russian company Neftgas and ExxonMobil. The operator, Exxon Neftgas Ltd., awarded the EPC contract (Engineering, Procurement & Construction) to the Norwegian Company Aker Solutions, who contracted NGI for geotechnical analysis and design of the foundation of the platform. The installation of the platform on site is planned for 2012.

The Arkutun-Dagi platform is a gravity base structure (GBS) with a base consisting of an enormous concrete caisson resting directly at the sea floor. Underneath the caisson, steel walls or "skirts" in a cross pattern penetrate about two metre down into the sea bed. These skirts will keep the platform stable in place horizontally. On top of the caisson, four tall shafts will carry the topside construction of 40 000 ton with process facilities and other equipment.

NGI's role as responsible for geotechnical design, dis the interpretation and evaluation of all site investigations and analysed the stability, bearing capacity and settlement under wave, ice and earthquake loading.

Finite element analysis of the loads on the Arkutun-Dagi platform in the Okhotsk Sea east of Sakhalin.