Geophysical and Geotechnical Considerations - … · Offshore Wind Workshop Geophysical and Geotechnical Considerations for U.S. Offshore Wind Development Workshop on Offshore …

June 2014 © Slide #1 McNeilan & Associates

DOE-DOI Offshore Wind

Workshop

Geophysical and Geotechnical Considerationsfor U.S. Offshore Wind Development

Workshop on Offshore Wind EnergyStandards and GuidelinesArlington, VA – June 2014

Tom McNeilan, McNeilan & Associates [email protected]



WorkshopG&G Program Requirements & Uses

Required for:• Geologic hazards evaluations and definition of site suitability & risks• Engineering design (foundation type selection, foundation design,

cable routing and design)• Regulatory permitting (to obtain approvals of COP and FIP permits)• Predicting foundation & foundation installation costs (and schedule)• Defining installation requirements• Understanding & managing project riskLinkages to other siting studies• Environmental• Archaeological• Met-Ocean (wind, wave, current, and ice loads and hazards)Separate or Integrated?• Tasks• Through project lifetime

Integration allows 1 + 1 + 1 + 1 = 8

Different entities (owner, engineer, BOEM, etc.) place different priorities on these

different requirements



WorkshopEuropean Experience

What are the lessons to be learned from OW in Europe?• Many early projects (in the early/mid 2000s) suffered from poor quality,

incomplete, or untimely AOS data Poor or inappropriate designs Couldn’t be installed with planned equipment Created delays (with associated cost increases) Optimum wind turbines not matched to local conditions Produced energy less than & more expensive than expected

• Significant improvements as industry matured, but …….• Crown Estate’s Offshore Wind Cost Pathway Studies continues to

advocate more investment for quality data earlier Suggest increasing pre-financial close investment by 5% for

earlier & more complete G&G studies can save up to 10 % to 20% of project capital cost



Workshop

Northern Europe OW Industry+ open ocean experience+ offshore wind experience– lack of BOEM experience– not local

East Coast Marine Industry– waterfront, not open ocean– no offshore wind experience– no BOEM experience+ local

Gulf of Mexico O&G Industry+ open ocean experience– no offshore wind experience+ BOEM experience– not local

Conclusion:Experience from all 3

sides of triangle must be merged and integrated

Sources of Applicable Expertise



WorkshopBOEM – GGARCH Guidelines

BOEM’s GGARCH Guidelines for Geophysical, Geotechnical & Archaeological Surveys• Derived from U.S. O&G and other offshore wind experience,

Guidelines & Standards

• Note what is missing – typical East Coast waterfront “marine” practices and methods

• Current November 2012 version due to be updated



WorkshopBOEM – GGARCH Guidelines

BOEM’s GGARCH Guidelines for Geophysical, Geotechnical & Archaeological Surveys• Current version includes different approaches for different elements of

minimum expectations for G&G (& Arch) activities

• Guideline minimums are often are viewed as being “this is what is required.”

Guideline Element 100% Prescriptive

100% Performance

basedArchaeological Requirements Geophysical DataGeological Interp & ReportGeotechnical Data & ReportEngineering Analyses & Report



WorkshopKey Considerations

Key Geological and Foundation Considerations• Seafloor Irregularity, Sediment Mobility & Scour

• Subsurface Variability & Channeling

• Dynamic Response of Turbine – Tower – Foundation System• Foundation Installation Uncertainties Much of Offshore Wind Project

Risks Lies in the Ground



WorkshopGeophysical Surveys

What is required for a high quality & successful survey?• Suitable Vessel with appropriate line keeping and

Adequate berthing Adequate deck space and deployment systems Area for data collection, QA/QC, and archiving Acoustically quiet

• Appropriate systems Multi-beam bathymetry Side scan sonar and magnetometer Chirp sub-bottom profiler Mid-penetration seismic reflection system –

Sound source & Hydrophone (array)• Appropriate deployment geometry and operational sequencing• Skilled and experienced operators and data processers• Appropriate safety and marine mammal avoidance procedures

Systems geometry and firing timing are

underappreciated keys to high quality data



WorkshopGeophysical Surveys

What are the most important geophysical data? Difference between “commodity data” & “value added data”

• MBES – Seafloor conditions & morphology. Sediment mobility.• SSS & Magnetometer – seafloor conditions, artifacts and target.• Chirp & Mid-penetration Seismic Reflection (boomer) – Sub-surface

geology and stratigraphy. Extrapolation between Borings.

System Relative Complexity Relative Value Relative Cost

MBES BathymetrySide Scan SonarMagnetometerChirp Sub-bottomMid-Pen Boomer



Workshop

MBES Quality is determined by;• System Choice & Beam Pattern• Water Depth• Vessel Speed

Multi-beam Data Quality



Workshop

MBES Data for Sediment Mobility• Fishermens Energy – NJ State Lands Project –

Comparison of Pre- and Post-Sandy Bathymetry

Multi-beam Data Examples

Pre- & post-Sandy data acquired by Alpine Ocean Seismic Survey under contract to Fishermens Energy

2011 profile across ridgePost-Sandy profile across the ridgePost-Sandy hydrographic contoursColors show bathymetric change

Legend for bathymetric change colors –—>



Workshop

MBES Data for Sediment Mobility• Virginia WEA – Comparison between 2013 regional survey lines and

2011 full-coverage NOAA mapping

`

Multi-beam Data Examples

2013 data acquired by Fugro under contract to Virginia DMME and BOEM

2011 NOAA full-coverage data, bathymetry rendering

2013 MBES swath width showing elevation change

Color palette for elevation change shownat right:



Workshop

Seismic Reflection Data Acquisition Process4.5m

Navigation

Antenna

CRP

24-Channel Hydrophone

Tail Buoy

(1.56 m Group Interval)

Single-Plate Boomer

SHORT ARRAY STREAMER

Tow Depth – 0.3 m

12.0 m6.25 m35.9 m

WATER

DENSE SAND

SOFT CLAY

“Boomer” seismic energy source “fires” ~ every 5 feet along vessel trackline Energy passes through water column and some reflects off seafloor and is recorded by hydrophonesOther energy passes reflects off deeper layers & is recorded by hydrophonesThese “reflections” appear as “reflectors” on the seismic data

Wavelet- +

American Polarity

Seismic Reflection Data Acquisition



Workshop

Subsurface with “nested” paleochannelsNegative amplitude reflection

Slide 2

Positive amplitude reflections

Seismic Reflection Example



Workshop

Geophysical Seismic Reflection Data Comparison • Comparison of typical single-plate, single-channel boomer data (left) &

multi-plate, multi-channel boomer data (right)

Minimum imaging depth required by BOEM

Seismic Reflection Data Examples

Vertical & horizontal scales of records are adjusted to be equalAqua arrows point to common locationYellow arrows point to water bottom multiplesTan arrowed bar shows depth of usable dataData are from Mid Atlantic OCS

Both are “boomer” data? how to specify what is required ?



Workshop

Geotechnical Drilling Vessels and Platforms• Jack-up – suitable to possibly ~18m water depth• Four-point anchor vessel with center-well• Land drilling rig on barge (for comparison)

Photos are at approximately equal scale

Geotechnical Exploration



Workshop

Geotechnical Sampling & Testing • In situ testing (left) & on-board lab testing (right) is standard procedure

• Down-hole systems(above) andtethered seafloorsystems (right)




Workshop

Geotechnical In Situ Testing• In Situ Testing is not explicitly required by

GGARCH, but is standard of practice in Europe


I would rather have 60 CPTs and 10 borings

than a ~ equal cost 20 to 25 borings only



Workshop

Interpretation Expectations• Maps and cross-sections that display conditions

& their variability to manage subsurface risks anddefine engineering properties & their variations

Integrated Interpretation

Virginia WEA Subsurface feature Map prepared by Fugro under contract to Virginia DMME and BOEM



WorkshopEpilogue

Or as said in Europe ….all projects pay for a quality G&G program ̶

whether one is conducted …. or not

Data RiskUncertainty Cost

Increased knowledgereduces uncertainty toreduce cost and risk

Documents

Geophysical and Geotechnical Considerations - … · Offshore Wind Workshop Geophysical and Geotechnical Considerations for U.S. Offshore Wind Development Workshop on Offshore …