Unexploded Ordnance; not so simple
Stuart Rickett, Peter McCusker, Marcel Sunier, Craig Harwood
EDF Energy Renewables, London, UK
The Blyth Offshore Demonstrator (BOD) consists of five MVOW V164 WTGs installed on Gravity Based Foundations with 66KV export and inter array cables.
As for all offshore wind farms, in order to minimise installation risk at the offshore site it is necessary to undertake surveys of the seabed for unexploded ordnance (UXO), complete inspection of any anomalies found and dispose of any confirmed UXO within the requirements set out in the Marine Licence.
During the development of BOD certain assumptions were made about the prevalence of likely UXO at the site. This was based upon early stage site details gathered during the consenting process which indicated the site would be a relatively low risk.
Following a detailed UXO site survey, BOD discovered significantly more potential UXO present than was forecasted. As BOD is a fast track project in terms of the deadline to get first power after FID, the post FID discovery of in excess of 700 "targets" within the deployment area became a real challenge in terms of both budget and programme due predominantly to contracting and consenting issues. Therefore BOD had to amend its UXO strategy.
The surveyed area has a high level of magnetic shielding due to dredge dumping from the nearby Port of Blyth and other dumping from the former power station and marine vessels over the years.
A flexible approach was required to contracting and consenting and this flexibility proved vital for the work to take place at all and certainly to conclude successfully.
It became obvious that an adaption of old technology could be utilised in a more concentrated fashion (acoustic profiling) to ease the uncertainty associated with the standard magnetometer derivation of targets and reduce the associated costs.
Ways of better defining what actually presented a threat as opposed to simple scrap and power station slag were investigated. The outcome of these investigations was that the independent UXO specialist carried out additional processing to remove some of the magnetic shielding and the project added PanGeo SBI works to the scope of the UXO investigation and clearance contract.
Immediate engagement with the consenting authorities on varying the licence was seen as prudent as this process proved to be on the critical path once engagement had taken place.
Through the adoption of a flexible approach BOD was able to adapt quickly to the issues discovered during the detailed site investigation.
The use of adapted and additional techniques enabled risk to be mitigated to manageable levels in terms of programme and contracting.
Working closely and openly with the consenting authorities allowed progress to be made quickly to ensure that consent amendments did not impact the projects critical path.
In addition, the investigation and detonation contractor replaced the proposed vessel with a newly attained one due to better operating criteria, which proved to be a very good choice, with the vessel continuing to work through seas as high as four metres whilst still being able to give a lee for the launch of the ROV.
Although the work was resource demanding, in order to meet the requirements of the program and consent needs, the use of a good contracting strategy and Contractor proved that this type of work can be managed successfully whilst not shortcutting the normal processes such as risk, safety and financial management.
The timing issues were managed with respect to consents and the investigations themselves but it has to be said that without the ability to provide quick decisions, chose the right Contractor and constant communications with the authorities it would not have been successful.
The main body of the presentation will briefly identify the pitfalls and benefits of UXO investigations as experienced on the BOD project.
Specific lessons that will be provided include:
Carry out the UXO survey as early as possible and certainly before FID - the money spent early will not only give greater clarity to the post FID budget but will give a full view of the possible issues early enough to be planned into the work stream for the project.
Early engagement and constant communications with the authorities is vital to prevent expensive delays.
Use a substantial DP vessel for the investigations; downtime on weather causes programme extension and needs resourcing.
The use of PanGeo SBI reduced the target count in this instance by a third.