Presentasjon

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Why is scientific work in geohazard important -
where does Geohazard fit in to oil business?
Presented by James M. Strout
Assessment - Prevention - Mitigation
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GEOHAZARDS, WHAT ARE THEY? Events caused by
geological conditions or processes, which
represent serious threats for human lives,
property or the natural environment
Onshore Volcanism Earthquakes Slides/debris
flows Floods Avalanches
Offshore Slope instability Earthquakes Tsunamis Sh
allow gas/hydrates Diapirism
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INTERNATIONAL CENTRE FOR GEOHAZARDSAssessment,
prevention, mitigation and management
ICG vision Develop knowledge that can help save
lives and reduce material and environmental
damage. To be, within 5 to 8 years, the world
authority and the premier research group on
geo-related natural hazards, with special
emphasis on slide hazards, both on land and
offshore.
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PARTNERS IN CENTRE OF EXCELLENCE
HOST ORGANISATION Norwegian Geotechnical
Institute (NGI) PARTNERS University of Oslo
(UiO) NTNU Geological Survey of Norway
(NGU) NORSAR
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Offshore geohazards
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Focus on underwater slope stability

• Field development on the continental slopes
• Enormous historic and paleo slides observed
• Large runout distances, retrogressive sliding
  upslope/laterally and tsunami generation may
  threaten 3rd parties in large areas

The Ormen lange field illustrates the importance
of a geohazard study
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The Storegga Slide (8200 ybp)
Ormen Lange
Field development was contingent on the results
of the geohazards study. It was necessary to -
understand the Storegga slide - survey, sample,
test and monitor to characterise site - develop
failure mechanisms and models - evaluate the
present day stability conditions These studies
resulted in the conclusion that the present day
slopes were stable, and the site was safe for
development.
Headwall 300 km Run-out ? 800 km Volume ?
5.600 km3 Area ? 34.000 km2
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Geohazards study elements

• Site investigation (geophysical, geological
  geotechnical)
• Assess in situ conditions and material properties
• Define relevant and critical geo-processes
• Assess interaction of processes
• Identify failure mechanisms
• Identify trigger mechanisms

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Geohazards study Assessment

• Overall geological understanding of site
• Assessment of probability of occurence
• Calculate/predict consequences
• Uncertainties
• Limited site investigations, measurement and test
  data
• Modelling of processes and mechanisms

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Monitoring and measuring

• Key parameters needed
• Seismic survey and metaocean data
• Geological structures, history, sedimentation
  rates
• Pore pressure and mechanical behaviour of the
  soil
• Inclination/movement/settlement/subsidence
• Gas releases or seepages
• Vibrations/earthquakes
• Time dependent variable?
• Snapshot measurement w/o time history
• Monitoring w/ time history, e.g. to capture
  natural variations, or effects caused by
  construction/production activity
• Timing before, during and after field
  development

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Closing comments

• Consequences of geohazard events can be very
  large, in terms of both project risk and 3rd
  party risk
• Thorough understanding of natural and human
  induced effects is needed in order to identify
  the failure scenarios relevant for field
  development
• Geohazard assessment require multi-discipline
  geoscience cooperation and understanding

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Purpose of geohazards research

• improve our understanding of why geohazards
  happen.
• assess the risks posed by geohazards.
• prevent the risks when possible.
• mitigate and manage the risks when it is not
  possible to prevent them.

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Thank your for your attention!
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Overheads illustrating each element of a
geohazard study
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Geophysical investigationImproved imaging
techniques
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In situ conditions and material
propertiesCorrelation of geological,
geotechnical, and geophysical parameters
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Defining critical geo-processes1D Basin model
for Pressure-Temperature time history during
geological time
Deposition rate
Ttemperature phydr. water pressure upore
pressure svertical soil stress seff. soil
stress
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Contributing processes/interactionGas hydrate
melting caused by climate change after
deglaciation
Geothermal gradient 50?C/km
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Failure mechanismRetrogressive Sliding

• Development of material and mechanical models
  required for explanation of failure on low slope
  angles
• High excess pore pressure and/or strain softening
  (brittleness) required
• Local downslope failure (slumping) need to be
  triggered for initation of large slide

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Triggering mechanisms Earthquake analysis

• 1D site response analysis of infinite slope
• Material model for cyclic loading includes pore
  pressure generation, cyclic shear strain,
  accumulated shear strain
• Pore pressure redistribution and dissipation
  after earthquake

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Overall geological understandingOrmen lange the
entire geo-conditions leading to instability
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Evaluate consequencesTsunami modelling and
prediction
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Evaluating probabilities

• Variability/incompleteness of data
• Modelling errors
• Recurrence of triggering mechanisms
• Presence of necessary conditions