Abstract
As the demand for energy resources continues to grow, the oil and gas industry is looking north for the discovery and extraction of offshore hydrocarbon resources. The Arctic region has significant discovered and undiscovered hydrocarbon resources and is an important area for energy development. In these cold areas however, the integrity of offshore structures such as pipelines is at risk from various geohazards. Burial under the seabed is the common practice of protecting offshore pipelines and these pipelines are often installed as bundles for many reasons including economic considerations, short installation windows, and technical issues. A bundle configuration can decrease the cost of project by reducing the installation time to one season and they may have certain design advantages.
Bundles have been used in all of the developments utilizing subsea pipelines offshore the North Slope of Alaska. In this paper, the state of practice of analyzing buried pipelines using pipe-soil-interaction elements on individual pipelines is extended to account for the effects of the different pipelines in the bundle. By modeling the individual pipelines in the bundle as opposed to an equivalent pipeline, it is possible to have a more accurate load distribution in the system and define the pipe-soil interaction more realistically. In addition, the behavior of each pipeline can be examined separately in the bundle.
One common geohazard of Arctic and subarctic regions, permafrost thaw settlement, is introduced and its effects on pipeline bundles are studied through FE models and compared with methods used in past projects. When analyzing permafrost thaw settlementin the past, each pipeline was modelled separately. These assumptions could result in inaccuracies due to the pipe-pipe, and bundle-soil interactions which cannot be modelled on an individual pipe. The newly developed finite element models couple the individual pipe-soil interactions together with the pipe-pipe interactions and provide a more accurate assessment of the pipeline and bundle behavior, which in turn can reduce potential conservatism in designs.
