Ice rubble generation for offshore production structures : Current practices overview

摘要

Ice Rubble Generators and Ice Protection Structures (IRG and IPS, respectively), if successful, would have a major impact on the economics of an offshore production structure in the Beaufort Sea. A hybrid design of these structures has the potential to reduce ice loads by stabilizing the ice rubble surrounding offshore structures during the winter, and by providing a depth-limiting mechanism for summer ice floes. The use of a year-round passive load-reduction technology would significantly reduce the ice loads, which would result in a lower-cost structure. With lower-cost structures, this enables more timely development of frontier gas reserves. Additionally, by both lowering the loads on offshore structures and helping to control the distribution of ice surrounding such structures, the environmental integrity of the protected structure(s) may be increased, leading to increased safety for onboard personnel. This report researches the state-of-the-art use of IRG and IPS to examine innovative technological concepts concerning these structures. The research assembles available information on protective structures that have generated rubble. The information was assembled through a literature review and discussions with national and international personnel involved in the past or at present with this type of work. The majority of structures investigated were designed for use in shallow (approximately 4 m) of water. However a number of concepts show the potential to be adapted for deeper water use. Structures specifically designed to generate rubble have focused on rubblemound berm or barge-based structures, which, although costly for deep water, appear to hold the most promise for a number of locations in the Canadian Beaufort Sea. Additionally, an arrangement of piles designed to hold back rubble or to encourage the formation of a stable ice sheet, comprised of highly loaded torsion piles, could be suitable for the Canadian Arctic. This research will provide guidance for the model test program in Year 2 of the CCTII UGS project, in terms of both concepts and physical size of the generators. The work carried out in this project may encourage the incorporation of a hybrid IRG/IPS into structurally sound design practices for the retrieval of unconventional gas supplies in the Canadian Beaufort Sea.