Platform Decommissioning Trends
- N.R. Anthony (Andersen Consulting) | B.F. Ronalds (U. of Western Australia) | E. Fakas (U. of Western Australia)
- Document ID
- Society of Petroleum Engineers
- SPE Asia Pacific Oil and Gas Conference and Exhibition, 16-18 October, Brisbane, Australia
- Publication Date
- Document Type
- Conference Paper
- 2000. Society of Petroleum Engineers
- 4.2.4 Risers, 5.6.4 Drillstem/Well Testing, 4.2 Pipelines, Flowlines and Risers, 4.2.3 Materials and Corrosion, 4.5 Offshore Facilities and Subsea Systems, 4.3.4 Scale, 4.5.3 Floating Production Systems, 4.5.5 Installation Equipment and Techniques
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Offshore oil and gas decommissioning experience to date, along with future trends, are explored by platform type and by region. There has been considerable decommissioning activity in the Gulf of Mexico, but generally only for small jacket and caisson structures. Partial removal, toppling, reuse and alternative use as an artificial reef are all common destinations of decommissioned platforms. In the North Sea, complete removal has been the preferred option, and this includes the largest platform chosen for decommissioning to date. Forthcoming cases including large concrete platforms will test this trend. Numerous floating facilities have been decommissioned in the North Sea and the majority have found reuse. Operators are also attempting to sell decommissioned North Sea jackets of moderate age.
Infrastructure offshore Australia is much less developed in comparison with the Gulf of Mexico and the North Sea and offshore facilities are smaller than the largest fixed steel and concrete platforms found elsewhere. Nonetheless, the largest jackets decommissioned to date around the world are only one-third the size of Australia's largest platforms. The local industry will watch with interest as decommissioning trends evolve in the early part of the 21st Century.
The decommissioning of offshore oil and gas platforms is an issue of growing concern within the industry as many fields approach the end of their economic lives, and although a rapid rise in recent decommissioning activity has afforded the industry some experience with smaller platforms, there is still much to learn and accomplish on a larger scale. Various options for decommissioning offshore structures and facilities exist. These options are driven by environmental considerations, cost, health and safety, available technology and politics (Ref. 1). The Gulf of Mexico and North Sea offer the greatest concentration and variety of offshore platforms, and decommissioning trends in these areas of the world will set precedents for growing oil and gas regions such as Australia to follow.
Of the order of 10,000 offshore facilities have been installed worldwide in the past 50 years. The installations are diverse in nature, including steel or concrete platforms, fixed or floating production systems, and offshore storage and loading facilities. Each is different, presenting its own challenges in terms of water depth, configuration and size (Ref. 2). Approximately 90% of installations are located in water depths less than 75m. The majority are steel jacket structures; they range in weight up to 45,000t and are in water depths up to 412m (Bullwinkle, Fig. 1). Some concrete gravity structures (CGS's) are an order of magnitude heavier than this and pose their own unique decommissioning problems, with the largest concrete platforms weighing over 700,000t. The Gulf of Mexico has many light jackets along with the deepest water jackets in the world. The North Sea also has both small and large jackets, often with very heavy topsides, and the largest concrete gravity structures. Fixed platforms (ie. jackets and CGS's) represent the greatest difficulty while moored/tethered facilities are generally the least difficult to decommission, due to the nature of their design.
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