Decision-making for offshore resource development

Fuglem, Mark (1997) Decision-making for offshore resource development. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (31MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The amount of oil in Canada which can be accessed economically is in decline, and industry is making a significant effort to find and develop alternative sources. The discovery of oil on the Grand Banks off Canada’s east coast is one notable success. While the reserves there are significant, the environment is very harsh, including high sea states and the presence of icebergs. Special designs are required for safe operations under these conditions and therefore production costs are high. -- The goal of this research is to develop a methodology for optimizing the choice and design of production systems for ice environments, given the two main criteria of safety and economic feasibility. Two specific objectives are addressed. The first objective is the development of an overall probabilistic methodology for assessing required design oads ad economic viability of proposed developments. Possible systems include large gravity based platforms which will withstand iceberg impacts, and floating systems which will be moved out of the way when icebergs approach. Design loads are determined by estimating the distribution of loads appropriate for each system and choosing the structural design which reduces the probability of failure. For gravity-based platforms, the design loads must accommodate impact with large icebergs which cannot be towed. For floating systems, the design loads must accommodate impact with smaller icebergs which cannot be detected during storm conditions. To determine appropriate design loads, a probabilistic model is developed which accounts for the number of icebergs encountered, the reliability of detection and avoidance schemes, and the impact dynamics including ice failure pressures. To compare the economic viability of different systems, cost-revenue models are developed and the netpre3sent values compared. The preferred system is one which maximizes revenues while minimizing costs, accounting for the time value of money given other potential investments. -- The second objective of this thesis is to evaluate the current use of Bayesian techniques in applied sciences and to suggest extensions to handle more complex problems. In applications involving complex systems, uncertainties in processes and in measurement of input parameters are common, therefore considerable use of judgement is required. It is important that these uncertainties are properly considered in design and economic evaluations. Specific areas of consideration include evaluation of the effect of improper choice of prior distributions and likelihood functions, incorporation of judgement when biases in measurement techniques are suspected, and the use of partial exchangeability as a mathematical method for incorporating one’s judgement regarding an overall probabilistic model. -- The modes developed for determining design loads are illustrated for a GBS and a floating production system. In both cases, it is found that the ice failure model used has a significant influence. In the case of the GBS, ice management had a negligible effect on design loads. In the case of the FPSO, the success of detection, management and avoidance system is very important. In particular, it was found that the reliability of the mooring disconnect system could significantly affect the required design loads.

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