Review of the risk assessment of buoyancy loss (RABL) project
This report presents a review of the Norwegian 'Risk Assessment of Buoyancy Loss' (RABL) project, completed in 1988. RABL was undertaken in the aftermath of the Alexander L. Kielland and Ocean Ranger accidents. RABL's stated purpose was to investigate causes of loss of buoyancy of semisubmersible drilling platforms, with the overall objective of developing an analytical procedure for consideration of buoyancy loss. This procedure was intended to be analogous to guidelines applied to fixed platforms in Norwegian waters. RABL demonstrated that it is practical to carry out a risk assessment of buoyancy loss for semisubmersibles. The RABL methodology and procedure were considered to be robust and sensitive to differences between concepts, and RABL recommended that the new analysis methodology should be used to assess safety levels for new platform designs, or for existing platforms subject to changes in operational premises. This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy. ISBN 0 7176 2729 2 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. iv v EXECUTIVE SUMMARY This report presents a review of the Norwegian 'Risk Assessment of Buoyancy Loss' (RABL) project, completed in 1988. RABL was undertaken in the aftermath of the Alexander L. Kielland and Ocean Ranger accidents. RABL's stated purpose was to investigate causes of loss of buoyancy of semi-submersible drilling platforms, with the overall objective of developing an analytical procedure for consideration of buoyancy loss. This procedure was intended to be analogous to guidelines applied to fixed platforms in Norwegian waters. RABL demonstrated that it is practical to carry out a risk assessment of buoyancy loss for semi-submersibles. The RABL methodology and procedure were considered to be robust and sensitive to differences between concepts, and RABL recommended that the new analysis methodology should be used to assess safety levels for new platform designs, or for existing platforms subject to changes in operational premises. RABL found that the main hazards were ship collisions, ballast system failures and blowouts. Technical recommendations were made on each of these aspects. RABL concluded that upper-deck reserve buoyancy (as required by NMD) provides …
Risk modelling of collision between supply ships and oil- and gas installations
This thesis is a framework for risk influence modelling of supply vessel-platform collisions, with the inclusion of central concepts from the Risk OMT model. The framework is a improvement from existing QRA frameworks in the sense that it has taken recent collisions into consideration, and enabled the opportunity to do risk influence modelling for the calculation of site specific risk. It can also be used as a tool for risk management, when the risk influences have been quantified. This model provides no quantifications, but it makes a good foundation for future work. The thesis incorporates knowledge from recent, representative collisions on the Norwegian Continental Shelf (NCS), and considered the guidelines and official safety procedures. This has been used to make three generic collision scenarios are general enough to take all probable collisions into account and at the same time be specific enough to account for the chains of events in previous accidents. These generic collision scenarios has been analysed with event tree analysis (ETA) and fault tree analysis (FTA) to identify and break down the operational barrier functions available to prevent collisions. A large set of risk influencing factors (RIFs) have been identified to be used to express the failure rate probabilities of the basic events found the FTA. These have been included from many different sources, to ensure that all significant RIFs are presented.
Numerical Simulation for Natural State of Two-Phase Liquid Dominated Geothermal Reservoir with Steam Cap Underlying Brine Reservoir
Hydrothermal reservoir which liquid-dominated hydrothermal reservoir is a type of geothermal reservoir that most widely used for power plant. The exploitation of mass and heat from the geothermal fluid will decrease the pressure in the reservoir over time. Therefore the pressure drop in the reservoir will have an impact on the formation of boiling zones or boiling will increase. The impacts are an increase in the fraction of steam, dryness, in the reservoir and with good vertical permeability will form a steam cap underlying the brine reservoir. The two- phase liquid dominated reservoir is sensitive to the porosity and difficult to assign average properties of the entire reservoir when there is boiling zone in some area of the reservoir. These paper showed successful development of two-phase liquid dominated geothermal reservoir and discussed the formation of steam cap above brine reservoir through numerical simulation for state natural conditions. The natural state modeling in steam cap shows a match with the conceptual model of the vapor-dominated developed. These paper also proofed the presence of transition zone, boiling zone, between steam cap and brine reservoir.