General Introduction
As the offshore industry approaches a stage at which many fixed offshore installations will reach the end of their oil and gas related ‘productive’ life, it is our aim to establish the technical and economic feasibility of re-using these installations as platforms to generate electricity using Offshore Wind Energy Converters (OWEC) and other Renewable Energy Systems (RES).
Overview
Decommissioning Fixed Offshore Installations
Following the Brent Spar affair of 1995, the economic, technical and environmental impacts of decommissioning offshore facilities by either dumping them on the seabed or bringing them onshore for incineration was studied in depth by many offshore operators, Governments and environmental scientists. It has since been established that the major concerns associated with decommissioning fixed steel or concrete offshore installations are:
- Cost: £8 billion to decommission North Sea structures and between £250-£1500 million of taxpayers money over 30 years.
- Energy Required: to remove one large structure can equate to the energy requirement of the city of Aberdeen for one month.
- Technical Feasibility: is an unknown quantity as structures can be as high as the Eiffel Tower and weigh 3 times more and removal is known to be complicated.
- Environmental Impact: which can include CO2 emissions from the incineration of metals onshore and leaching of environmentally unfriendly chemicals on the seabed.
Decommissioning is one of the biggest threats to profitability facing the offshore oil and gas industry in coming years and under current legislation, nearly 95% of the worlds existing offshore installations must be completely removed in the next 30 years - at a cost of £40bn.
Many structures have been constructed with a fatigue life of 100 years and have been designed to withstand winds in excess of 100 miles per hour and storm ocean waves as high as 30 m so there still could be a very significant working life left in certain facilities. Due to the benefits achieved by using an existing infrastucture for as long as is feasibly possible, previous studies have been carried out to establish alternatives to oil and gas related duties.
Offshore Wind Power & other Renewable Energy Systems
Interest in renewable energy resources to generate electricity is on the increase for the following reasons:
- Increasing global energy requirements
- Depleting fossil fuel reserves
- Harmful emissions from fossil fuel.
- Fluctuating price of oil.
- Pressure by International Agreement to decrease current levels of emissions to 1990 levels by the year 2010.
Offshore wind power in particular has been a source of energy for the generation of electricity in the Dutch sector of the North Sea since summer 1991 and sites are currently earmarked for development around the UK shoreline.
It has been established that the advantages of the generation of electricity by offshore wind turbines are:
- Less visual and noise impact.
- Higher wind speed than onshore (up to 20% higher).
- Less turbulent wind conditions therefore less fatigue on equipment.
The development of large wind turbines offshore is however proving expensive due to the high cost of installing offshore concrete foundations (50% of overall project cost) which confirmed the fact that existing offshore structures which are no longer required for oil and gas related duties should be reviewed for this purpose.
Based on our knowledge of energy systems and the environment, we decided to investigate the potential of re-using the basic installation, further to the removal of oil & gas exploration equipment from the topside, to site OWEC and other RES which may prove to be an environmentally friendly cost-effective option, in certain circumstances.
Maximising Potential Energy Resources
To maximise the amount of electricity which could be generated from an offshore installation a review of current and developing technologies would be carried out in order to exploit the potential of the vast renewable energy resources available offshore. The electricity could be transmitted onshore and sold to the network or converted into valuable marketable commodities on the facility and distributed by existing pipelines.
Processes
It was identified that the cost of electrical cable installation could render the re-use of farshore installations un-viable (£2 - 5 Million per km). It was then decided to investigate the possibility of re-using the existing infrastrucuture of pipelines to distribute the electricity in a liquid or gas form. In addition, the transmission and storage of the electricity generated from RES is not efficient due to the intermittent nature of many renewable energy resources. We identified that the following electicity conversion processes which required further investigation were:
- Potable water produced by desalination
- Hydrogen & Oxygen produced by electrolysis.
Employment
There are obviously job opportunities connected with the dismantling of offshore installations however these 'jobs' are short lived due to the nature of decommissioning i.e when all installations are decommissioned there will be few further opportunities.
Diversification into a more progressive market will enable offshore operators to gain valuable experience and create careers in the field of renewable energy. It is believed that UK ship-yards could become sites for the manufacturing of offshore wind turbines and large scale wave machines, as they already possess world-leading experience and leading edge technology to deal with offshore operations.
