IN BRIEF

The Geo People provide consultants for the installation of offshore wind turbines and tidal energy infrastructure.

Site/hazard surveys are required prior to installation of foundations to ensure that the characteristics of the subsurface are strong and safe enough to build the required structure for wind and tidal projects. Our client representatives are on board to ensure that the acquisition is carried out to the client’s specifications.

During the process of pile driving for the foundations of turbine towers in shallow water and jackets in deeper water, the resulting noise has to be controlled to minimise the risk of harm to marine life. Our marine mammal observers and passive acoustic monitoring observers monitor the specified area for wildlife in accordance to the local guidelines, minimising the disturbance caused by piling noise.

Cable laying is carried out during the installation of new wind turbines to transfer the energy from source to land. Our cable laying QCs verify that the approved procedures are followed and that the inspections and testing records are completed.

All of these services provided for offshore wind and tidal energies, are transferred from our extensive experience of supplying these services to the oil & gas industry.

IN DETAIL

Offshore wind power

The power generated by a wind turbine is a function of the cube of the windspeed, with power output increasing up to a maximum output for the particular turbine. Modern utility-scale wind turbines range from around 600kW to 5MW of rated power, with turbines of rated output of 1.5-3MW becoming the most common in commercial use. Wind power is growing at a rate of 30% annually and had a worldwide installed capacity of 238,351 megawatts (MW) at the end of 2011. It is widely used in Europe, Asia and the United States. Several countries have achieved relatively high levels of wind power penetration, such as 21% of stationary electricity production in Denmark, 18% in Portugal, 16% in Spain, 14% in Ireland and 9% in Germany in 2010. As of 2011, 83 countries around the world are using wind power on a commercial basis. In 2013, wind generated almost 3% of the world’s total electricity. The long term technical potential of wind energy is believed to be five times the total current global energy production, or 40 times current electricity demand, assuming all practical barriers were overcome. This output scale would require wind turbines to be installed over large areas, particularly in areas of higher wind resources, such as offshore. As offshore wind speeds are, on average, about 190% of that on land, offshore resources can contribute substantially more energy than land stationed turbines. Therefore, those areas where winds are stronger and more constant, such as offshore and high altitude sites, are preferred locations for wind farms. In these locations, typical capacity factors are 20-40%, with values at the upper end of the range in particularly favourable sites.

Site/hazard survey QC for offshore wind and tidal

For site/hazard surveys, the primary objectives of the consultant for QC are to define any shallow gas hazards and buried river channels, to map any highly fractured zones that may result in excessive mud losses or indicate historic slumping, to accurately define the bathymetry, particularly in the region of the proposed structure, and to identify any debris, or cables on the site. There is a legal and operational need for detailed information about the seabed and the geological layers immediately below it in the vicinity of the proposed turbine tower/jacket or tidal infrastructure prior to construction. This is so that the equipment and anchors will function properly and not encounter potentially fatal gas pockets or buried river channels.

The technique used for the high resolution site survey is the same as for conventional 2D seismic but with a smaller source typically 40 to 400ci. Sometimes a sparker is used for the source with its energy coming from an electrical discharge. As we are only looking at the top few layers of the sediments, only a short streamer is used, between 600 and 1200m. In order for the higher frequencies and high resolution image to be acquired, the streamer is towed at a smaller depth below the surface, so acquisition has to take place in relatively calm weather conditions. Side scan sonar is used to determine the texture, topography and character of seabed sediments as well as locate debris, boulders, outcrops, pipelines and other equipment on or just below the sea floor. The operating frequency varies depending on manufacturer and intended purpose. Multibeam echo sounders are used to verify the side scan sonar data and provide densely sampled digital terrain models to further define the topography and assist in planning the location of pipelines, turbine towers/jackets and tidal infrastructure. The boomer, an electro-mechanical system producing a low power, high frequency, acoustic pulse for a high resolution image of near surface sedimentary layers is sometimes used as a source. Now replacing the boomer, the chirp profiler, a small marine vibrator, is preferable as it provides a more consistent acoustic input signal. For physical tests, sea floor coring is carried out for determining the conditions of the seabed.

The Geo People provide site/hazard survey QC for infrastructure and cable laying QC for offshore wind and tidal energy projects. Survey duration is typically 4-5 days, although due to weather and logistics in the marine environment, this is frequently more. At the end of each project, the client representative produces a final QC report including an executive summary, QC test results, procedures, a description of problems, QC techniques, decisions, time accountability, communications, recommendations, and a detailed account of the survey. The Geo People understand the importance of the final report and ensures that these are received by the client within the specified time frame.

MMO for offshore wind

During offshore construction projects, one of the environmental concerns is the noise produced from seismic airguns and piling. The pressure waves can potentially disturb marine life in particular cetaceans which use sound to communicate with one another and locate food. Marine mammal observers, passive acoustic monitors with PAM equipment are frequently deployed, although seabird observers are sometimes required. 

Marine mammal observers (MMOs) and passive acoustic monitoring observers (PAMs) are employed on site surveys prior to jacket/tower installation and during piling for the wind turbine jacket/tower, when marine life is subjected to the noise of vibro-piling or hydraulic hammers. The exclusion zone in UK waters is 500m as for conventional seismic surveys and the MMO may be on a separate boat so calculating where the sightings are and their direction of travel relative to the source is not straight forward. MMOs use high-powered 7x50 marine binoculars with reticules, for monitoring for at least 30 minutes (or for one hour in deep water) prior to and during soft start procedures and during the acquisition or piling. Their role is to ensure that the JNCC or other guidelines appropriate for the country of operation are followed and that the events and any non-compliances are logged.

MMOs and PSOs from The Geo People are graduates in marine biology or environmental (or related) science. They are trained in the use of JNCC (Joint Nature Conservation Committee) guidelines, and additional guidelines appropriate to the country of operation, ensuring that guidelines and special recommendations are adhered to by the seismic contractor. There are a number of MMO courses available. The website of the Marine Mammal Observer Association (MMOA), is a good place to search for courses. The Geo People is a proud corporate sponsor of the MMOA.

PAM for offshore wind

During times of poor visibility, passive acoustic monitoring (PAM) equipment is used to detect clicks, whistles and moans from cetaceans. MMOs report on the protected species mitigation survey efforts and ensure that the requirements set forth by the guidelines for minimising acoustic disturbance and injury to marine mammals from seismic surveys are fulfilled. Marine life such as seals, whales, dolphins, porpoises and sea turtles may be all referred to in the guidelines. In addition to keeping noise levels at the lowest practicable levels, the recommendations contained in the guidelines will assist in ensuring that marine life, in areas of proposed airgun/piling activity are protected against possible injury.

The Geo People provides PAM (passive acoustic monitoring) equipment with 100% redundancy for use during night time operations or in the day when visibility is poor. PAM operators are able to deploy this equipment during mobilisation and pack up on completion ready for shipping back, checking all the equipment on the inventory. The Night Hawk III system from MSeis Ltd is what we commonly use. Again, good MMO and PAM courses may be found on the MMOA website.