Evaluation of concepts for loading of hydrocarbons in ice-infested waters

Abstract

The thesis deals with topics related to the evaluation of concepts for loading and transport of hydrocarbons from ice-infested waters at a chosen location in the Pechora Sea (Eastern Barents Sea). Exploitation of hydrocarbons in the Arctic is quite novel. The export of the products may either take place by pipelines from the offshore area to a suitable land location and transport from there over land, or via a terminal offshore by tankers to the market. In remote areas such as the Pechora Sea an export solution by tankers is quite attractive both for the offshore and onshore fields. The reason is lower initial investment costs compared to an export solution over land where new pipelines are required, and secondly due to short access to international waters where longterm rules and regulations apply. These aspects are the impetus behind the aspects highlighted in the thesis.

Present experience is considered important in the evaluation of loading and transport concepts and the thesis gives an overview of some important experiences of oil field development in ice-infested waters. From this point a more general overview of the environmental conditions and characteristics of the Pechora Sea is presented, and this is used for a screening of possible development solutions for offshore oil loading in the area. Also transport solutions of oil to the market are briefly commented. The Pechora Sea also makes the basis for experimental work related to feasibility of sub-sea solutions that are considered the most potential solutions when evaluating the development costs and risks. Several topics related to a sub-sea solution are investigated such as mooring loads, operations related to offshore loading and ice impact on the sub-sea system. As part of my work experiments were done in the ice basin at Hamburgische Schiffbau-Versuchsanstalt (HSVA) in

Germany. The tests were done with an Arctic Shuttle Barge system that consisted of a pusher unit and an oil barge with a submerged turret loading system (STL). An important part of these tests was to investigate the ice impact on the sub-sea system, and aspects related to measured ice impact on the moorings are presented. The loads from available test series prior to the Arctic Shuttle Barge testing are also compared with data on a moored exploration vessel, Kulluk, that was operating in the Beaufort Sea in the 1980’s.

Further, the work includes model testing and comparison of model tests and full-scale results from the Kulluk vessel. Models of first-year sea ice ridges and scaling and measurement of strength properties are important in ice model testing. This part of the work also presents topics on modelling of ridges and testing of strength parameters. The scaling process is also considered and findings regarding rubble testing and consolidated layer strengths are presented.