Dossier Océan et énergie - Énergie Thermique des Mers
Sommaire IOA News Letters
The U.K. includes OTEC/DOWA in the Marine Technology Energy Foresight Programme
This article summarizes the work of the Energy Sub Group of the Marine Technology Foresight programme. The final report was compiled by DAVID McKENZIE, formerly Chief Executive of the Marine Technology Directorate. The full text of the report can be found in the Journal of the Society for Underwater Technology (issue 4, 1997).
The Marine Foresight Panel came about in 1995 to represent the cross-cutting interests of the Marine Markets as the sixteenth panel in the UK Government¡¦s Technology Foresight exercise. The Technology Foresight process was set up as a national consultation exercise to bring together industry, academia and Government to determine where the country should invest its science engineering and technology spending.
The first task of the Sub-Group was to define a Foresight objective for marine energy which was: To position the UK to become the world¡¦s leading supplier of marine-based energy technology, by securing a long-term domestic supply of economical, marine-based energy and developing an associated major export industry in technology and services which will be competitive and influential in world energy economics.
Energy was one of the industry sectors covered by the original Foresight exercise. The Marine Energy Sub-Group of the newly-formed Marine Panel, therefore, had a ready-prepared report which, while not seeking to identify specific marine items, had identified a number of areas which were closely allied to the marine industries. The Natural Resources, Agriculture and Environmental Panel also identified topics directly relevant to the Sub-Group¡¦s work; however, while encompassing the findings of these two reports, the sub-group decided that they would work from the list of marine sector activities generated from two meetings held in 1994, one in Southampton and one in Aberdeen. The sub-group also decided to confine its deliberations to those areas where the marine environment was a primary influence; thus, in general, geoscientific topics relevant to offshore oil and gas, while given very high priority in the Energy Report, are not considered further in this report.
This report summarizes the information received to date with more detailed Appendices supporting each of the technology sections; no attempt has been made, so far, to prioritize between various technologies. Clearly one important question is the weight to give to the emerging technologies associated with the sources of renewable, environmentally-friendly energy when considered alongside the continuing development of technology for the offshore oil and gas industry. It is hoped that a wider debate will ensure that the long term merits of marine renewable energy are carefully considered and taken into account when compared with the requirements of the oil and gas industry.
The technologies covered by the Group were: oil and gas, wind, waves, OTEC floating systems, DOWA, tides and currents, geothermal, biomass as energy source, bioremediation, environmental protection, structures, decommissioning, subsea operations, energy storage, energy transmission, supply and pipelines, logistics, communications, safety, human factors.
2. Future Energy Requirements
Some 75% of the surface of the globe is covered by sea and ocean, and today this environment supplies 25% of the oil and gas produced, and accounts for about the same proportion of the world total of known oil and gas reserves. For the future the seas and oceans of the world represent a vast source of non-polluting and renewable energy, and it has been estimated that if less than 0.1% of the renewable energy available within the oceans could be converted into electricity, it would satisfy the present world demand for energy more than five times over.
The world-wide growth in energy demand over the next 25 years may be as much as 70% above today¡¦s levels, and while current thinking suggests that fossil fuel supplies will meet most of this increased demand, new fuel sources will have to carry a progressively increasing share of the burden from about 2020 onwards. Any reduction in demand as a result of improved efficiency of energy utilization in the developed economics is expected to be more than offset by the rise in demand from the developing countries.
3. Marine Energy Sources
The sources of energy from the marine environment split into two distinct categories: the first is the existing international offshore oil and gas industry (Figure 1¡V Estimated total UK oil and gas production) which can be expected to continue to make incremental advances within the Foresight time frame. In the UK, this industry, together with its many supporting and service contractors, has undertaken a major assault on both its capital and operating costs over the last few years and is competitive at oil prices of $15 a barrel or less. It is now embarking on developments in the deeper and more hostile waters west of the Shetland Islands and is positioning itself to continue production into the third decade of the next century.
The second category is the development of new sources of renewable energy from the marine environment, namely wind, wave, tidal, and ocean thermal conversion. Some of these technologies are very new and some at more advanced stages of development. There does not appear to be a strong drive to promote the economic development of these technologies within the Foresight time-scale. They do, however, represent possible future opportunities for UK industry if the technologies can be developed to be ready to meet the changing energy markets of the next century.
3.1 Offshore oil and gas
3.1.1 Technology challenges for oil and gas
The technological challenges can be summarized as:
|No 'dry holes' exploration effectiveness|
|Increased reservoir yield: effective exploitation|
|Safe and cost-effective productive|
|Optimized utilization of existing infrastructure|
|Multiple field developments|
|Drilling and well productivity|
Specific targets, to be achieved within the Foresight timescale, could include:
|Achieve at least 80% rate of drilling success|
|Reduce unrecovered hydrocarbons by 50%|
|Develop process and intervention technology for entire hydrocarbon production and export operation to be subsea|
|Develop the technology for economic high capacity, minimal loss, long distance power transmission systems|
The offshore oil and gas industry accounted for 17% of UK industrial investment in 1994, contributed about 2% to the UK ¡¦ s GDP, and was also an important source of government tax revenues. Over the last three years the industry has undergone major changes as it has sought to implement the lessons arising from the CRINE (Cost Reduction In a New Era) initiative and reduce its costs and establish new working practices. One of the areas that has been under focus has been the need for new technology and from where it should be obtained. Much work has been done in identifying the requirements for Research and Development, and the views of the exploration and production companies, technology delivery companies, and government bodies have been well documented. A broad consensus exists over technology priorities and key areas for development.
The Energy Panel, in its report, gave priority recommendations to two specific aspects of the oil and gas industry, which were high hit rate exploration techniques and increased yields from existing hydrocarbon reservoirs (Figure 2 ¡V Discovery of reserves found per exploration well). The Energy Panel also identified ¡¥ drilling for oil and gas ¡¦ and ¡¥ low cost oil/gas production including platform and pipeline construction/maintenance ¡¦ as being important targets but of lower priority.
The ANRE (Agriculture Natural Resources and Environment) panel pointed out that new technologies had been an integral part of the North Sea success and that the UK needed to maintain its leading position in hydrocarbon technologies through continued research, technological development and demonstration. In the marine area, the ANRE panel particularly identified remote and subsea technologies as key areas for development, with very deep-water fields, far from land, as being one of the prime targets. In its deliberations, and working from the marine position, the Sub-Group has identified many of the same areas as both the Energy and ANRE panels but, in general, has excluded the geoscience based technologies.
Environmental aspects of offshore operations, and decommissioning especially, will become even more important during the Foresight time-scale. The costs and issues surrounding decommissioning may become major factors in determining the economic viability of projects, in both hydrocarbon and renewable energy production. There is scope for significant innovation in deriving methods for environmental protection and acceptable decommissioning techniques.
The main targets for construction technology are improvements in construction materials (lighter, stronger, cheaper and corrosion resistant), joining technologies particularly adhesives, expert design software to include such details as weld design, and advanced structures that self-adapt with one part carrying fatigue loads while another carries survival loads.
The ability to construct platforms rapidly, to tight schedules, and to find ways of having an all year round weather window for installation are important aims in seeking to keep costs down.
5. Floating Structures
5.1 Technology challenges for floating structures
Technology challenges for floating structures are summarized as:
|Deep-water mooring systems using light-weight materials ¡V important for OTEC|
|Xmas tree and wellhead systems|
|Dry xmas trees for floaters|
|Offshore gas conversion|
|Elimination of emissions|
|High pressure subsea pumps|
|Deepwater riser and umbilical systems|
Floating structures, either FPSOs (Floating Production Storage and Offloading) or TLPs (Tension Leg Platforms), are aimed primarily at overcoming the difficulties of deep water, down to 2500m, particularly in hostile environments. While they have different characteristics, much work needs to be done aimed at marrying their different strengths and increasing their depth range on:
|New concepts that provide both dry xmas trees and oil storage|
|Cheap, light, high stiffness materials for TLP tethers|
|Develop a full understanding of risers and moorings in depths greater than 1000m|
|Large diameter risers (or cold water pipes!) for FPSOs, either steel catenary, flexible, or hybrids|
|Economic offshore gas conversion and loading systems|
|Active condition monitoring for mooring lines, swivels, etc.|
|High and quantifiable reliability for all associated subsea components|
|Large diameter (>72 ¡¨) high pressure gas seals for swivels|
|Reduction in environmental emissions on tanker loading|
In order to compete with LNG (Liquefied Natural Gas) transportation, large diameter, deepwater, intercontinental pipelines need to be developed. This will involve work on collapse pressure behavior, manufacturing techniques, welding and pipelay technology. Associated with these developments will be the need to advance compressor technology to handle the pressures involved. Large diameter risers for use from floaters in water depths down to 2500m need to be developed, and the problems created by the axial tension due to the length of hanging pipe together with the environmental loads need to be solved economically.
The development of analysis and installation capabilities for large diameter pipelines and risers/umbilicals will also be of great assistance for OTEC cold water pipes and power/fresh water cables/hoses.
In-field flowlines could be recovered to be used again so methods need to be developed to reel such lines back onboard a barge. The cost of providing insulation on lines, particularly in deep water is a major factor and the supply of cheap, reliable chemicals to suppress hydrates remains a high priority.
6.1 Technology challenges ¡Ð pipelines and risers
|Large diameter lines ¡Ðdesign, manufacture, laying|
|Materials for deepwater continuous lay|
|Advanced welding technology|
|Cheap, strong, lightweight insulation materials|
|Deepwater flexible risers|
|Motion compensation systems|
|Very large diameter seals for high pressure gas swivels|
New pipeline materials that compete with steel on cost, yet are quick and easy to lay, need to be identified and tested; the development of one-shot welding technology to speed up laying processes is also required. But with any new materials, as for current materials, reliable inspection tools are required for all sizes of pipeline, and the ability to coat corroded lines internally to extend their lives would be a major step forward.
Sub-surface innovations over recent years, for instance in seismic, drilling and completion technologies, have all contributed greatly to the potential of subsea business opportunities. However, there is scope for the subsea industry to be increasingly pro-active in recognizing these sub-surface trends and the opportunities they offer.
Given the obvious trend towards conversion of exploration wells into producers, and to subsequent appraisal through phased production, it is vital to incorporate increased flexibility into the subsea system without significantly driving up either cost or complexity. A key element in this quest will be increased reliance on modular components with standard interfaces.
To achieve the true objective of Foresight, it is necessary to break free from conventional thinking, towards achievement of challenging stretch targets by the year 2020 or sooner. For instance, plans could be generated to develop remote offshore fields by completely eliminating surface facilities. This, combined with the ability to transmit power over long distances with minimal losses, will revolutionize conventional wisdom about the conversion of offshore hydrocarbon resources into power for industrial and domestic consumption.
8. Seabed Hydrates
Very little work has been done, so far, to develop seabed hydrates as a potential source of energy. Up to now, hydrates have been seen as a potential safety hazard in drilling, only very recently are companies beginning to appreciate their energy potential. The traditional methods of exploration, basin and reservoir analysis techniques do not apply and a complete range of new technologies needs to be developed. In particular what is now needed is a long-term joint program involving industry, academia and government agencies carrying out fundamental work aimed at: understanding the potential resource, carrying out a regional appraisal of the distribution and evaluating the potential for the UK, and developing an ability to extract gas from clathrates in a controlled way.
9. Renewable Resources
The renewable sources of marine energy that have been considered are: offshore wind, wave, tide and marine currents, and offshore thermal energy conversion (OTEC) and deep ocean water applications (DOWA).
In the Energy Report these sources of energy received only ¡¥watching brief ¡¦ status and in the DTI document New and Renewable Energy ¡Ð Future prospects for the UK, a number of the onshore renewable technologies are identified as having reached the ¡¥ market enablement ¡¦ stage, and some are still at the assessment stage, but all the marine sources of energy again received only ¡¥ watching brief ¡¦ status.
UK government policy is to stimulate the development of new and renewable energy sources wherever they have prospects of being economically attractive and environmentally acceptable in order to contribute to: diverse, secure and sustainable energy supplies, reduction in the emission of pollutants, and encouragement of internationally competitive industries.
In doing this, it will take account of those factors which influence business competitiveness and work towards 1500MW of new electrical generating capacity, from renewable sources, for the UK by 2000.
In nearly all areas in the development of marine energy sources, the technologies have been developed to the stage where they need assistance with demonstrator projects. Such projects are aimed either at initial proof of concept, or at proving that the current state of technology is commercially viable and obtaining a good understanding for realistic construction costs. Much work has been done and continues to be done with funding from both industry and the European Commission. Without some official backing from the UK government, however, the attraction of funds will be difficult and the opportunities which exist today to develop competitive industries for the future may soon be lost.
A number of organizations and universities are working on the development of the technology necessary to exploit sources of marine renewable energy. Without government input, however, there is no focus for their efforts. One way of achieving this would be for the government, jointly with the European Commission and industry, to set up in the UK a Centre for Marine Energy Technology. Besides providing a centre of expertise for the world to draw on, it would allow the UK to adopt a pro-active stance in the search for long-term, environmentally friendly energy sources.
One of the characteristics of marine renewable energy is that it is generated in locations which are far from main centres of population and industrial activity. This means that once the energy has reached the shoreline, the appropriate grid facilities need to be put in place if they do not currently exist, as is the case in the north west of Scotland. Another of the characteristics is the variable or cyclic nature of most, but not all, renewable marine energy. Even where renewable energy is feeding small local communities the question of smoothing cyclic variations can arise and a storage capability is needed. Development of cheap transmission systems, both over land and sea, and energy storage systems, will assist the development of marine renewables.
The possibility of marine biomass as a source of marine renewable energy has also been considered. Although there have been schemes to produce energy from marine biomass, kelp and fish, it is considered that it is unlikely that such a source could ever make a significant contribution to UK energy requirements. For remote island communities energy from kelp might be an option but it would have to compete with the other forms of available renewable energy. Further investigation into the use of marine biomass has not been pursued further in this report.
9.1 Offshore wind energy
Weather patterns in the Northern Hemisphere result in the UK having one of the best wind resources in N.W. Europe and the technology is well developed in the country and worldwide. However, onshore there are a significant number of perceived environmental disadvantages to wind farms such as their physical size, visual impact and noise levels, in addition to possible land usage limitations. Such problems need not arise in the development of the offshore wind resource where wind speeds are generally greater.
The problems faced by offshore wind generation which would benefit from further research and development are: marinisation of plant, design for low maintenance, offshore platform design, and energy storage.
With the exception of energy storage these are areas of technology with which the UK ¡¦ s offshore oil and gas industry is familiar. It is particularly important that the lessons recently learnt on the design, manufacture and installation of low cost offshore structures aretransferred to the offshore wind industry so that studies can be updated using current best practice and a good estimate made of the cost of offshore wind power made. The various studies should then be updated or redone and progress might then be possible on the construction of a prototype offshore wind farm.
Offshore wind energy buoys could provide a source of power for oil industry subsea developments and encouragement needs to be given for further study work in this area.
9.2 Wave energy
The principal offshore wave energy levels for the UK are high because of the long distance across the Atlantic where the winds interact on the ocean surface; however, the shadowing effect of Ireland on the coasts of England and Wales is significant. The wave energy resource may be subdivided into:
|shoreline: where the device is constructed on the seashore|
|near-shore: where the device is floating or bottom mounted in 10-25m of water|
|offshore: where the device is moored in greater than 40m water depth|
The major constraints on the full exploitation of near-shore and offshore devices would be the effects on shipping and fisheries combined with the need for power cables to shore.
A second generation shoreline device, LIMPET, designed by Queens University, Belfast, is seeking Joule funding to build a prototype. This device overcomes many of the problems that were encountered with the first prototype on Islay, in the Inner Hebrides, which is supplying power to the grid. ART Ltd., from Inverness, hope to install a near-shore prototype device, OSPREY, (Ocean Swell Power Renewable Energy Device) next year. OSPREY is a combined 2 MW swell plus 1.5 MW wind generator and will be gravity anchored 300-400m offshore near Dounreay. These devices, although only at demonstrator stages, are claimed to be able to produce electricity at competitive prices today. If this can be borne out practically, then many assumptions will be challenged and the picture will need to be reassessed.(Editor ¡¦ s note ¡V OSPREY was lost during installation, however, ART plan to install an improved design.)
Fundamental work on energy transfer systems using high pressure hydraulics and sloped buoys is being carried out by Edinburgh University. This work will need to be proven on near-shore devices although in the longer term it is aimed at offshore devices. At current low levels of funding it is likely to be at least ten years before the demonstrator project stage is reached providing the research interest can be maintained.
What is now needed, if the niche markets that are now beginning to appear overseas are to be exploited by UK companies, is support for the LIMPET and OSPREY demonstrator projects and longer term support for the ongoing work at Edinburgh University.
9.3 Tidal and marine current energy
The UK has a number of sites where the potential exists for the generation of electricity using high velocity tidal currents with the best sites in the Pentland Firth and the Channel Islands. The total resource available would amount to about 19% of the electricity used in the UK, in 1991.
While the exploitation of marine currents is based on well established technology, and hence has less uncertainty about it, there has been very little work carried out in the world on proof of concept. What is now needed is a single, small-scale pilot project to confirm present assumptions, gain operational experience and give greater confidence in cost estimates.
The following areas are in need of research and development: tidal stream turbine (tidemill) design and testing, high current location and seabed fixture systems of platforms, subsea cabling in high current conditions, and economic deployment systems. Tidal power is predictable but cyclic and so tidal power systems will benefit substantially from the availability of energy storage systems to smooth output.
9.4 Offshore Thermal Energy Conversion (OTEC) ¡V compiled by Martin Brown and Jeremy Fletcher
OTEC is dependent upon warm surface water and hence it is confined to the waters between the tropics of Cancer and Capricorn. A number of small-scale pilot projects have been built around the world but so far no MW-sized net output demonstrator projects have been undertaken. The prime contenders for this technology are small islands particularly in the Pacific Ocean, the Indian Ocean and the Caribbean, with Hawaii and Taiwan leading the development of the technology.
Multi-product plants, perhaps utilizing deep ocean water applications (DOWA), are likely to be most cost effective where electricity is only one of a number of products. A potential advantage of OTEC when compared with the other ¡§ renewables ¡¨ is that it produces a continuous flow of power for base-load purposes whereas the other systems generate energy which is variable with time, and for which coincidence with peak load requirements is most unlikely and hence some form of energy storage facility would be required.
Work over the last twenty years has brought OTEC/DOWA to the stage where the construction of a MW-sized demonstrator plant is needed either onshore or offshore. It is considered that a review with industry should be carried out to establish in which niche areas of OTEC technologies the UK may still be able to develop future markets, and which of the UK dependencies would provide a target for a demonstrator project. A programme should then be formulated to carry out the demonstrator project with the support of the local community and which will provide the springboard for industry into the new markets (see Appendix A).
Appendix A: OTEC and DOWA
A.1 Ocean Thermal Energy Conversion (OTEC)
OTEC has relevance to the UK since this country still has a number of dependencies in the Caribbean, Pacific, Atlantic and Indian oceans that are suitable for OTEC. This has become of increasing importance since the ratification of the UN Law of the Sea Convention in November1994 by the European commission. This entitles island nations to large Exclusive Economic Zones. In addition, from the EU perspective, France and the Netherlands also have a number of dependencies in prime OTEC locations.
FPSO developments, e.g., deepwater turret mooring, standardized low cost fabrication, etc., have great long-term potential for OTEC. Large floating OTEC vessels could provide a major export market plus offshore design and fabrication jobs. This ties in with the UK ¡¦ s established position as a leader in offshore oil and gas technology.
Niche markets: OTEC is already economic for remote island states, but these do not have the required financial resources for such a project. The UK government should provide funding for a demonstration project on a British dependency.
OTEC can provide a number of associated products, (see DOWA below). However, for island states, one of the most valuable, apart from electricity, is the production of fresh water. The economics of OTEC are improved when fresh water production is included in the equation. Basically OTEC comprises very simple technology (particularly when compared with nuclear power) and all the individual components have been tested over the years. There is now a need for a 5MW government funded pilot plant to obtain reliable operational performance figures.
Work over the last 20 years has brought OTEC to the stage where the construction of a MW-sized demonstrator plant is needed either onshore or offshore.
Those areas where research and development are currently needed are: heat exchanger design, low pressure turbine design for open-cycle, cold water pipe design, low cost floating platform, high capacity submerged seawater pumps and moorings for deep water.
There is potential to combine wind energy with OTEC (5MW-size plant to improve cost effectiveness) and make maximum use of infrastructure (transmission lines, etc.)
A.2 Deep Ocean Water Applications (DOWA)
DOWA applications include:
|Efficiency enhancement of conventional coastal thermal power and desalination systems. This is very promising particularly for new build power stations in the Far East. A market survey needs to be financed by the government to assess the size of the potential market and to publicize this concept.|
|Air conditioning using Deep Ocean water. A thermodynamically efficient system with great potential for applications such as tourist hotel complexes on tourist islands. Government encouragement/publicity for this environmentally friendly application is required. Whoever gets in first will be in a dominant position in what promises to be a reasonably sized market.|
|Aquaculture using Deep Ocean water. This water is much richer in nutrients and free of pathogens compared with surface water and hence is ideal for aquaculture. The Natural Energy Laboratory of Hawaii, and associated private enterprises, have proved the benefits that can be obtained from Deep Ocean water. This technology has potential to assist the economies of island nations providing an additional source of export revenue (e.g., sale of high value shellfish). Such a venture can be combined with an OTEC electricity/fresh water plant.|
|Agriculture. By running cold Deep Ocean water through small pipes just below the surface of the soil it is possible to irrigate crops by condensation of water vapour out of the air. In addition, crops used to cooler climates can be grown in areas of high sunshine resulting in faster growth rates. Such a proposal is probably not feasible alone, but is an attractive earner for an OTEC electricity/fresh water/aquaculture complex complete with deep ocean air conditioning. Again this concept has been demonstrated at the National Energy Laboratory in Hawaii.|
Basically there is a need for government funding to get operational experience from a pilot plant from which extrapolation can be made to larger plants, i.e. a Technology Demonstrator Project (TDP) Program. This might be achieved by TDP tax incentives.
Appendix B ¡V Energy Sub-Group Members
Mr. David McKenzie, Dr. D. Ardus, Mr. K. Avrin, Prof. M.J. Baker, Mr. Martin G. Brown, Dr. S. Brown, Mrs. A.D. Cox, Dr. P. Dunn, Prof. R. Eatock-Taylor, Mr. Jeremy B. Fletcher, Mr. J. Foote, Dr. P. Kingston, Mr. T. Lazenby, Miss A. Longley, Mr. J. Loughhead, Mr. M. Murphy, Dr R. Rayner, Mr. S.F. Schuyleman, Dr, D. Smith.