Offshore pipelines in cold regions - Environmental loadings & geotechnical considerations

Abstract

With the oil industry's continued quest for oil and gas in frontier offshore locations, several developments have taken place in regions characterized by seasonal ice cover including the US Beaufort, North Caspian, and Sakhalin Island. In these projects, pipeline transp ortation systems have been used, which are a cost-effective, safe and reliable mode of hydrocarbon transport to shore. One of the key design issues is ice gouging that affects engineering considerations with respect to strain based design, target burial depth requirements, cost and safety. It is generally accepted that offshore pipelines in ice environments will need to be trenched and backfilled for protection. Burial depths can be greater than those that might normally be required for pipelines in temperate climates. Burial depth requirements will be a function of the design ice gouge depth (to prevent interaction between the ice and pipe) and an acceptable level of subgouge deformation beneath a gouging ice keel (which strains the pipeline). There still exists uncertainty on the magnitude and extent of subgouge soil deformations due to ice gouging and the importance of sediment transport mechanisms for biasing gouge statistics. Pushing the limits to developments further offshore in deeper Arctic waters (i.e. 15 to 50m water depth) will require that additional consideration be given to aspects related to pipeline design, in particular with respect to burial for protection against ice gouging.