Why is scientific work in geohazard important - where does Geohazard fit in to oil business
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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. GEOHAZARDS, WHAT ARE THEY?

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Assessment - Prevention - Mitigation

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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


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

Shallow gas/hydrates

Diapirism


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.


PARTNERS IN CENTRE OF EXCELLENCE

  • HOST ORGANISATION

    • Norwegian Geotechnical Institute (NGI)

  • PARTNERS

    • University of Oslo (UiO)

    • NTNU

    • Geological Survey of Norway (NGU)

    • NORSAR


Wave generation

Tsunami

Tsunami

Retrogressive sliding

Mud volcano

Debris flow

Gas hydrates or free gas

Gas chimney

Earth-quake

Underground

blowout

Diapirism Doming

Overpressure

Offshore geohazards


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


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


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


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


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


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


Purpose of geohazards research

  • improve ourunderstanding 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.


Thank your for your attention!


Overheads illustrating each element of a geohazard study


Geophysical investigationImproved imaging techniques


In situ conditions and material propertiesCorrelation of geological, geotechnical, and geophysical parameters


h(t)

z

Sealevel change

time

Dt

s’

Du

p

u

s

T

Stress/pressure: p, s, u, s’

Defining critical geo-processes1D Basin model for Pressure-Temperature time history during geological time

Deposition rate

T=temperature

p=hydr. water pressure

u=pore pressure

s=vertical soil stress

s’=eff. soil stress


BGHSZ at LGM sea level at -130m m

Potential zone of GH melting

BGHZ after intrusion

of warm atlantic surface water

BGHSZ after sea level rise

Contributing processes/interactionGas hydrate melting caused by climate change after deglaciation

Geothermal gradient 50C/km


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


0.05g

0.10g

0.20g

0.30g

Depth belom mudline, m

Depth belom mudline, m

Max. pore pressure ratio after event, %

Max. displacement, cm

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


Overall geological understandingOrmen lange: the entire “geo-conditions” leading to instability


Evaluate consequencesTsunami modelling and prediction


Evaluating probabilities

  • Variability/incompleteness of data

  • Modelling errors

  • Recurrence of triggering mechanisms

  • Presence of necessary conditions

  • + + +


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