Offshore Wind Farms (OWF) Horns Rev 3 and Kriegers Flak Geo Investigations 2012-2013
Presentation of the two OWF sites and planning of surveys
- presented by Stig Berendt Marstal, Energinet.dk
Geophysical pre-investigations and geological models
- presented by Stig Berendt Marstal, Energinet.dk assisted by Jon Steer, ex-GEMS
Geotechnical pre-investigations and UXO studies
Agenda - Geo Investigations 2012-2013
1. Location and delineation of the two OWF areas
2. Instruction from Energistyrelsen – Danish Energy Agency - to Energinet.dk – Danish TSO - to plan and carry out pre-
investigations (EIA and geo investigations) for the two areas
3. Main purposes of the OWF Geo Investigations
4. The results of the Geophysical pre-investigations in 2012
5. Planning of Geotechnical pre-investigations 2013
The purpose of this MEETING is to give YOU – the potential OWF
bidders – an overview of the status of the Geo Investigations, and
for us to get some feedback from YOU on especially the plans for
the geotechnical pre-investigations in 2013.
Location and delineation of the two OWF areas
Overall planning areas for Horns Rev 3 and Kriegers Flak OWFs [Screening 2011]
Water depths Shipping lanes Distance to harbours
Location and delineation of Horns Rev 3 in the North Sea
Facts and Factors considered:
Relatively shallow waters between 10-20m depth North of OWF Horns Rev 2;
North of Horns Rev 2 cable;
South and west of pipelines Military exercise area
Shipping lanes
Distance to shore: 10–30km Distance to harbours: 25-55km
Black dashed polygon: Geophysical pre-investigation area, c. 220 km2 including buffers HR3 a “well-known” area due to OWF HR1 and HR2
What did we know about the areas before survey? HR3:
Some shipwrecks are known in the area (Nautical Chart, other observations)
A UXO danger zone according to the Nautical Chart
Some existing geo and metocean knowledge from the Horns Rev 2 site, including the EIA and site investigations. Lots of the latter material is restricted/confidential though
The Geological Survey of Denmark (GEUS) marine database and recent
scientific articles about the region including a conceptual model
What did we know about the areas before survey? HR3:
A conceptual geological model for the offshore area/region exists (based on relatively few and primarily single channel seismic surveys), see article:
Primarily sandy deposits (marine, glacial, interglacial) in a basin
Upper “basement” in basin made up by glacial deposits (Saalian till .
Some layers might be organic-rich: geotechnical challenges?
Location and delineation of Kriegers Flak in the Baltic
A bathymetric high - an inundated island
Water depths min.
15-25m within c. 150km2 bank Infrastructure (Baltic Cable) Sand abstraction area
Shipping lanes
Distance to shore 15km
Distance to harbour 20-40km German Baltic II OWF
Open stretches and lots of wind Grey: Geophysical pre-investigation area, c. 250 km2 including buffers
What did we know about the areas before survey? KF:
Varying water depths (25m and 28m highlighted)
Some shipwrecks but possibly no UXO
No cables and pipelines - BalticCable to the west, Gas pipe (red) considered
Swedish pre-investigations – German investigations, both classified
What did we know about the areas before survey? KF:
Some existing geo and metocean knowledge from the Swedish EIA and from non- confidential (20-30 year) GEUS reports regarding mineral resources
Seabed: Till and morainic ridges – residual sediments (boulders, gravel)
Late and post glacial: Periods of land (island) phase
Holocene and ongoing erosion and redeposition: Mineral resource – Sand abstraction
What did we know about the areas before survey? KF:
Area overridden by glaciers from easterly directions
Glacio-techtonised thrust faulted layers? (as on nearby Møns Klint)
Sedimentary bedrock: Limestone at depths between 10-40(+) m below seabed
At least two different tills; the lower expected to be very hard
Geological profiles, scientific article by Anjar et al
Summing up for both OWF areas
Relatively large pre-investigations areas, netto c. 200 km2, compared to what is actually needed for construction of 400 MW at Horns Rev 3 and 600 MW at Kriegers Flak:
• Flexibility during the pre-investigations, the results may lead to narrowing the areas before the tendering phase
• Flexibility for the forthcoming concession owner during the planning and construction of the OWFs
The following Desk Studys have been carried out / initiated:
• UXO
• MetOcean
• Geology and geotechnology
• Environmental and biology
• Marine Archaeology
Instruction from Danish Energy Agency (ENS) to ENDK
• 22 March 2012: New ambitious Energy Agreement in the Danish Parliament:
Increase the Danish electrical wind power from 25% to 50% in 2020:
2 new OWFs of 1,000 MW in total:
400 MW at Horns Rev 3.
600 MW at Kriegers Flak.
• 23 April 2012: Energinet.dk (TSO) was instructed by ENS to plan and manage the pre-investigations
• March 2013: Results of geophysical pre-investigations must be published.
• 2013: Geotechnical investigations.
• Winter 2013-Early 2014: All
investigations must be finalized and reported.
• 2013-2015: Government tender for
Primary purposes of the OWF geo investigations
• Necessary input to the marine EIA
―the EIAs for the OWFs and the export cables are to be completed and consented before the submission of tenders
• To achieve the sharpest and most qualified prices for the OWFs
―Assumption: the more the potential forthcoming concession owner knows about e.g. the seabed conditions, the lower are the risks of encountering unforeseen „problems‟ during the construction of the OWFs, including the installation and foundation activities, hence the lower the price for building the OWFs will be (and the lower the tender prices will be)
―[Megavind 2010] “….more comprehensive data, in particular wind, wave and soil data are needed to lower risks for future developers on selected sites.”
―[SIG SUT 2005, DNV 2004]: “A recent survey of European offshore wind farm projects concluded that c. 25% of total project capital expenditure could be directly attributed to the chosen foundation system. This fact alone highlights the importance of achieving an optimum foundation solution and thus the need for a focused and cost-effective site investigation.”
Assumption: When reducing the unknowns, lowest possible
price for construction and running the OWFs will be achieved.
Purposes and objectives of the geo investigations
According to the instructions from the Danish Energy Agency the overall purposes and objectives of the geological/geotechnical pre-investigations of the OWF areas are to gather data, information and knowledge about the seabed and the sub- bottom geology in order for the interested parties, including the potential OWF builders, to be able to:
• Delineate the areas for development of the OWFs (preliminary site selection and decision making)
• Preliminary plan the structures (including substations, wind turbines and cables.)
• Assess the feasibility of the use of jack-up platforms and anchor-based vessels during the investigation and construction phases.
• Preliminary plan and determine general requirements for foundation concepts, design and construction
• Carry out assessments of the environmental impacts on the seabed (EIA including e.g. possible impacts on possible layers / objects of marine archaeological interest).
However, it is naturally assumed that the winning OWF builder will carry out
Offshore Wind Farms
Horns Rev 3 and Kriegers Flak Geo Investigations 2012-2013
Geophysical pre-investigations and geological models
Preliminary results
But why carry out geophysical surveys in the first place?
Functional requirements to the outcome of the OWF geophysical survey (1):
Detailed mapping of the surface of the seabed in order to be able to:
1. To provide accurate bathymetric charts of the OWF pre-investigation area.
2. Chart surfaces and objects of biological relevance (e.g. possible stone reefs, bubble reefs, areas with high coverage of macroalgae and/or eelgrass).
3. Chart surfaces and objects of marine archaeological relevance (e.g. historical shipwrecks including anchors and related items, possible relics of ancient settlements).
4. Chart possible man-made obstructions (e.g. un-exploded ordnance (UXO), lost fishing gear, waste of any kind left on the sea bottom, possible uncharted cables and pipelines).
5. Chart natural seabed features, morphology and types (e.g. rocks, sand ripples, loose and mobile material, sandy surfaces, till surfaces, etc.).
6. Chart possible geohazards (very soft sediments, slides, gas etc.)
Functional requirements to the outcome of the OWF geophysical survey (2):
Mapping the subsurface in a sufficient level of details in order to be able to:
1. Map geological layers and structures to well below the expected maximum foundation
depths of wind turbines, which may extend down to c. 30-60m below seabed dependent of the local geological setting plus the foundation type.
2. Set up a preliminary 3D geological/stratigraphic model with geological information down to at least c. 100m below seabed (also for planning of the 2013 geotechnical program).
3. Identify potential areas of marine archaeological interest (shallow geological mapping of Holocene / Top glacial sediments/surfaces).
Geophysical challenges:
1. Shallow waters - seabed multiples often at the same level as the expected foundation depths.
2. At places: Hard dense layers and seabed – strong reflection – low penetration.
Geophysical Survey Tender 2012 - Operational Requirements
1. 100m line spacing: As a reasonable balancing between requirements, productivity and resolution, Energinet.dk selected an overall survey line spacing of 100m, and crossing lines every 1000m, in order to achieve:
- Full bathymetric seafloor coverage (MBES) – IHO order 1a
- Full side scan sonar coverage (SSS) – 200% coverage with 2 high frequencies
2. 3 SBP systems run 2 by 2:
- Relative high frequency SBP system (e.g. pinger) along every line
- Relative medium frequency SBP system (e.g. sparker) along every second line
- Relative low frequency multichannel SBP system (e.g. airgun) along every other second line
3. Magnetometer (gradiometers consisting of 2 magnetometers) along every line
4. 1x1km Grid: To establish a general overview in the two OWF areas of the geology plus acoustic possibilities and limitations, Energinet.dk has specified initial major gridlines of 1km x 1km to be surveyed. Based on the results of the initial major gridlines surveying, a detailed planning of exact line spacing plus survey parameters shall be carried out.
Geophysical Survey Tender 2012 – Digital Deliverables
MBES and SSS:
6 types GIS images in 0.1m x 0.1m pixel size i 1km x 1km GeoTiff files:
o MBES depths and MBES backscattering.
o Side Scan Sonar enlighted from two directions and with two frequencies 300/600 kHz.
MBES:
o Raw data and ungridded soundings, (X,Y,Z) values in CSV-format.
o Gridded soundings, 0.1m, 0,5 m and 5m resolution, ArcGIS ASCII grid file.
o Contour curves for the depth data, 0.5m curve interval, ArcGIS shape file.
SSS:
o Raw data as acquired XTF files.
SBP:
o Raw and processed data as SEGY
o Interpreted layers (X, Y, Z) values in CSV-format and isopach/elevation in ArcGIS format MAG
o Raw and processed data in CSV-format
Geodesy: Horizontal datum WGS84 UTM32N; Vertical reference DVR90
Geophysical 2012 – Offshore
•
The British survey company GEMS Survey Ltd. won the EU tender early July 2012 (Price, Quality, Time, Manning and Experience).
•
Very well-suited, well–equipped and well-manned vessel: MV Aquarius, on-board processing and interpretation facilities etc.
•
Energinet.dk Client rep. aboard.
•
OWF HR3 and OWF KF were finished, after less than 2½ months
surveying and hardly any WOW, by early October after achieving more
than 5000 line-km, generally very high data quality!
Geophysical 2012 - Onshore
•
Onshore processing, interpretation and reporting progressed, but became regrettably gradually more and more delayed
•
Also Management and Payment issues!
•
Something was very wrong! Nearshore vessel for Cable Route sent home.
•
On December 4th 2012 GEMS went into liquidation!
•
All personnel sent home, and all data kept in England!
•
DELAYS in data delivery and reporting, unavoidably
Financial and juridical negotiations with the Administrators during December
and January. Eventually, in early February 2013 Energinet.dk received the
QC‟ed and full datasets from OWF HR3 and KF!
Geophysical 2012 – delayed, but on the right track
• Processing, interpretation and reporting is now again on the right track, led, managed and carried out by Energinet.dk, Rambøll
Denmark and some handpicked ex-GEMS employees.
• However, final data delivery and reporting is delayed somewhat
o
By February 26
ththe two Survey Results Reports are received in draft
oOperational reports are also due with in very short time
o
By end of March data for the EIA will be ready in final versions
oFinal reporting and data delivery is planned/expected to be ready
before end of May!
Geophysical 2012 – Results from HR3:
HR3 Bathymetry based on R2Sonics 2024, dual head
Water depths: Range from 21m in the northern central section to 10m along a ridge towards the
HR3 Backscatter based on R2Sonics 2024, dual head
Backscatter: Amplitude data in grey scale, which yields useful information regarding the character of the seabed. The lighter records illustrate areas of higher amplitude indicative of more
consolidated and / or coarse sediments at the seabed. The record also provides useful information
HR3 Side Scan Sonar based on an Edgetech 4200 MP
SSS imagery of the seabed, including variations in seabed sediment type, seabed infrastructure
HR3 Side Scan Sonar based on an Edgetech 4200 MP
SSS: Isolated targets are identified and displayed in the seabed features chart. 185 targets in total.
A key target, also identified on the Admiralty Chart for the area, is provided in the high frequency side scan sonar water fall display. Due to the targets size, character and general character it is
HR3 Gradiometer – a Geometrics G882 transverse MAG array
MAG providing detection of ferrous (iron rich) objects at the seabed, along the survey line track.
Residual magnetic anomaly
HR3 Grab Samples - Van Veen grab sediment bite of 0.045m
2Forty nine (49) grab samples were recovered across the HR3 site, at locations chosen primarily from variations observed in the SSS mosaic but also based on the shallow geology pinger dataset.
The grab samples were analysed offshore and used to ground truth the interpretation and derive
HR3 Seabed Features based on the mentioned methods
Sediment type: Silty/clayey SAND to GRAVEL
HR3 Sub-bottom Geology and Geological Model
A hull-mounted 4x4 MASSA pinger array was used for detailed geological mapping of the shallow sub-bottom geology (base of HM1, HM2 and HF) limited by the strong first seabed multiple.
For the study of the deeper geology, a GeoEel 48-channel streamer was employed, in conjunction
HR3 Comments to the Geological Models
HR3 Geological Model 2012 is based on the existing model by GEUS. However, it has generally not been possible to identify and map the ”top glacial unconformity” during the 2012 survey (reflector C below, and the green line above), and therefore the top of the glacial units differs!
HR3 Base Holocene Marine 1 depth below seabed (BSB)
The upper Holocene Marine unit (HM1) comprises of loose, unconsolidated fine to medium marine SAND. This unit is present across the entire site excluding an area to the far west of the site, and is only present as a thin veneer to the far east. The unit thickens to a maximum of 7m below a north- south trending ridge towards the west of site centre. This corresponds with the shoaling observed
HR3 Holocene Marine 1 – termination to the west
HR3 Base Holocene Marine 2 depth below seabed (BSB)
The lower Holocene Marine unit (HM2) is of similar composition as HM1 but could potentially be finer grained. The unit is observed across the entire site excluding the zone to the far west.
HR3 Base Holocene Freshwater depth below seabed (BSB)
The Holocene Freshwater (HF) can be observed in channel forms at the base of HM2, incised up to
HR3 Holocene horizons HM1, HM2 and HF
In all profiles 0.01s can be assumed to represent 8.5m given a seismic velocity of 1700m/s. 100 shot points (horizontal scale) represents approximately 40m for the pinger datasets. All profiles are
HR3 Base Horns Rev Valley depth below seabed (BSB)
The Horns Rev Valley (HRV) is a Holocene depositional unit which is present to the west of site
HR3 Holocene horizons HM2 and HRV
In all profiles 0.01s can be assumed to represent 8.5m given a seismic velocity of 1700m/s. 100 shot points (horizontal scale) represents approximately 40m for the pinger datasets. All profiles are
HR3 Holocene horizons HM2 and HRV
HR3 Examples of Blanking and Phase reversals in HRV
A distinct area of data blanking has been observed in the sub-bottom data within the centre of the interpreted Horns Rev Valley. This is likely to represent an accumulation of soft organic matter at the base of the valley, including peat (gyttja) and potential gas. The sub-bottom data record in these locations is eradicated. In some instances seismic „phase reversal‟ is evident, another
HR3 Gas blanking
The top of the blanking, interpreted as at the shallowest depths has been digitised and the extent
HR3 Base Weichselian Meltwater depth below seabed (BSB)
The Weichselian Meltwater (WS) unit comprises of sediments deposited in an alluvial plain and
considering its seismic character is likely to comprise a mixture of fine grained sand, silts and clays.
The base of the unit has been identified towards the east of the site as a network of relatively shallow channels which reach a maximum thickness of 19m, but it is eroded and truncated by the
HR3 Base Eemian Marine depth below seabed (BSB)
The Eemian Marine (EM) unit is heterogeneous across the site and likely to comprise of silts and
HR3 Base Eemian Freshwater depth below seabed (BSB)
The Eemian Freshwater (EF) unit is visible as broad channel like features or undulations 25m deep at the base of the EM unit, eroded into the glacial deposits beneath. The top of this unit is not
clearly defined but forms part of the EM unit which overlies it. The EF unit in particular may contain organic matter, including thin peat layers however this is not clearly evident in the seismic record.
HR3 SGI and SG
HR3 Base SGI depth below seabed (BSB)
The Saalian Glacial Infill (SGI) unit can be observed incised into the underlying Saalian Glacial (SG) unit as two major and several smaller, interconnecting valley forms. The larger valleys are steeply sided and up to 250m deep, with a width of 2-4km. The structure is indicative of over-deepened tunnel valleys, formed as a function of glacial loadings and water flow in an environment of high
HR3 Boulders at/close to the seabed to the west
On the Side Scan Sonar data, it can be seen, that there is a concentration of boulders at the most
Deep over-deepened buried Quaternary (tunnel) valleys
From ”Overdeepened Quaternary valleys in the eastern Danish North Sea: morphology
HR3 Faults
HR3 Summing up the Geological Model
Unit Description Depth to Base
(meters BSB) Holocene Marine 1 (HM1) Blanket cover of loose fine-medium sand thickening
across a north-south seabed ridge
0-8
Holocene Marine 2 (HM2)
Blanket cover of likely finer grade sand 1-20 Holocene Freshwater (HF)
Localised channel infill of possibly soft, silts / clays 1-18 Horns Rev Valley (HRV) North-south channel infill of sands and interbedded
silts and clays. Possible organich-rich (peat, gyttja) and gasevidence at the base.
5-30
Weichselian Meltwater
(WS) Planar deposits of fine grade sand, silts and clays 2-35
Eemian Marine (EM) Silts and clays 2-40
Eemian Freshwater (EF)
Planar deposits of sands, silts and clays. Possible peat (Gyttja) and gas evidence at the base
8-35
Saalian Meltwater (SM)
Fine grade sand, silts and clays 15-30 Saalian Glacial (SGI) Irregular tunnel valley infill likely comprising a
chaotic mix of meltwater and glacial deposits, including tertiary blocks
15-335
Saalian Glacial (SG)
Glacial deposits, likely diamict of clay and including blocks and boulders
101-275
Geophysical 2012 – Results from KF:
KF Bathymetry based on R2Sonics 2024, dual head
Water depths: The water depths across the site range from 12m in the central and north eastern section deepening at the perimeter of the site to a maximum depth of 33m in the far south.
Seabed bedforms: Seabed bedforms are observed around the perimeter of the site associated with
KF Bathymetry based on R2Sonics 2024, dual head
Sediment ridges comprising of glacial till can be observed in the dataset, within which numerous
KF Backscatter based on R2Sonics 2024, dual head
Backscatter: Amplitude data in grey scale, which yields useful information regarding the character of the seabed. The lighter records illustrate areas of higher amplitude indicative of more
consolidated and / or coarse sediments at the seabed.
KF Side Scan Sonar based on an Edgetech 4200 MP
The side scan sonar was heavily influenced by the thermocline during the start of the survey
KF Side Scan Sonar based on an Edgetech 4200 MP
SSS: Isolated targets are identified and displayed in the seabed features chart; 4359 in total.
Of these 16 are potentially of man-made origin; all others have been assigned as boulders, which are dominant in the record, some of which measure up to 10m in diameter (left figure).
KF Combined SSS + MBES
3 potential wrecks are observed in the side scan sonar data, alongside the bathymetric datasets.
The sonar record of these three targets are provided in the
bathymetric and high frequency side scan sonar water fall displays to the right.
KF Gradiometer – a Geometrics G882 transverse MAG array
MAG providing detection of ferrous (iron rich) objects at the seabed, along the survey line track.
498 targets in total were identified, although still to be evaluated. Of these 4 are a function of the locality to the 3 observed wrecks and 26 are associated with seabed infrastructure (Baltic Cable).
It is likely that the numerous anomalies are a function of the ferrous properties of the observed
Residual magnetic anomaly
KF Combined Gradiometer and SSS
This Figure shows the same magnetic anomaly signature but overlain onto the side scan sonar
KF Grab Samples - Van Veen grab sediment bite of 0.045m
2134 grab samples were recovered across the KF3 site. The results show that the majority of the area is covered by sand however clay deposits are returned in areas where glacial till is expected at the seabed. Although the grab samples are believed to be representative, especially considering the number obtained, they could ultimately be biased as they are unlikely to return the stiffest
KF Seabed Features based on the mentioned methods
Sediment type: TILL to GRAVEL
KF Sub-bottom Geology and Geological Model
A hull-mounted 4x4 MASSA pinger array was used for detailed geological mapping of the shallow sub-bottom geology limited by the strong first seabed multiple.
For the study of the deeper geology, a GeoEel 48-channel streamer was employed, in conjunction
KF Comments to the Geological Model
Unit Description Depth to Base
(meters BSB) Holocene Marine 1
(HM1) Blanket cover of loose fine-medium sand 0-2m Holocene Marine 2
(HM2i) Internal Reflector
Loose fine-medium sand, showing
progradation to the west 0-8m
Holocene 3 (H3) Fine-medium sand within a spit, likely to be
more compacted than HM1 and HM2 0-12m Flow Till (FT)
Soft sands, clay and boulders less consolidated than the underlying tills from
which they derive
0-15m
Upper Till (UT)
Diamict of predominantly clay with gravel, cobbles and boulders but also occurrences of
silt and sand
0-23m
Kreigers Flak Clay (KFC)
Silts and clays residing localised in
depressions within the underlying LT 5-12m Lower Till (LT) Diamict of predominantly clay with gravel,
cobbles and numerous boulders 5-65m
Cretaceous (C) Soft Chalk Undetected
The sub-bottom geology has been interpreted (and is ongoing) and a realistic geological model for
KF Base Holocene Marine 1 depth below seabed (BSB)
The upper Holocene Marine unit (HM1) comprises of loose, unconsolidated marine SAND which provides a thin blanket cover across much of the site. It can be observed to thicken across site centre to a maximum of 2.5m. The unit is not observed in the geophysical record at exposures of the till units, however it is still likely to be present in most cases as a thin veneer.
KF Base Holocene Marine 2 & 3 depth below seabed (BSB)
The underlying Holocene Marine unit 2 (HM2) is observed to thicken across site centre, influenced
KF Base Holocene Marine 2i depth below seabed (BSB)
An internal reflector (HM2i) - its steep slope is indicative of a reflector within the progradational sequence, towards the west. HM2i may represent a distinct change in sediments at the interface, including occurrence of potential gravel or silts and clays.
KF Holocene layers HM1-HM3
KF Flow Till depth below seabed (BSB)
The Flow Till (FT) unit – base is light blue reflector - is present in the record infilling the irregular / undulating till unit which lies beneath the Holocene layers. These sediments consist of soft sands,
KF Pinger Seismic Section, Line 6103500. Weichselian Units
The Flow Till (FT) is present in the record infilling the irregular / undulating till unit which lies beneath. These sediments consist of soft sands, clay and boulders and are less consolidated than
KF Pinger Seismic Section, Line 6103500. Weichselian Units
The Kriegers Flak Clay (KFC) unit has not been interpreted at this stage in interpretation. It is believed to be present within the Kriegers Flak area as it is present in cores completed in the vicinity. It cannot be identified clearly as it is often deformed into the overlying UT unit or it has been completely eroded. At this stage the KFC base should be considered to be at the base of the
KF Upper Till depth below seabed (BSB)
KF Lower Till / Top of Cretaceous Chalk depth below seabed
This unit is regularly 15m thick,
although, about channel forms, it can approach 50m in thickness locally.
Or are these “channels” in fact results
Base Lower Till (LT) unit = Top of the Cretaceous Chalk.
The LT unit can be observed exposed at the seabed as clearly seen in the seabed features through the coarsening of
sediments and
increased number of boulders.
