Decommissioning offshore concrete platforms with an Executive Summary by Graham Morrison of the Health and Safety Executive Prepared by Atkins Process Limited and Olav Olsen A / S for the Health and Safety Executive 2003 RESEARCH REPORT 058

Decommissioning activity offshore is expected to increase significantly in the next few years and will include some very large concrete platforms in the northern North Sea. The two studies included in this report examine possible methods of removal and demolition, including complete removal, part-removal to below the water line and leaving the concrete bases in place after removing the topsides completely. The studies are prefaced by an introduction from the Health and Safety Executive into the legislative and technical issues that led to this research. The studies examine the risks to people and the environment from decommissioning large concrete platforms. The possibilities of refloating, transporting the structures to shore and disposing of them on land are all evaluated. The first study was carried out by Atkins Process in the UK, the second by Olav Olsen A/S consultants in Norway and the original designers of the Condeep platforms, the most common type of concrete platform offshore Europe. Both studies indicate that risks from removal could be very high and refloating may not be possible for some older platforms. For all options, risks of injury to personnel from subsea work, underwater cutting or structural collapse from overloading could exceed the normally accepted risk criteria unless these operations can be very carefully controlled. This report and the work it describes were funded by the HSE. Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the prior written permission of the copyright owner. The two Research Reports reported below have been completed recently that assess the risks to people and the enviroment from decommissioning concrete platforms. These studies assess the feasibility of refloating and disposing of the concrete bases of very large platforms of the types found offshore in northern Europe They examine the possible options for removal and demolition, considering the original design of the structures and their current condition and taking account of the present state of engineering knowledge and any likely future developments. One study was carried out by Atkins Process in the UK, the other by Olav Olsen consultants in Norway and the original designer of the Condeep platforms. Both Joint Industry Projects involved oil companies …