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? - PowerPoint PPT PresentationTRANSCRIPT
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Assessment - Prevention - Mitigation
Presented by James M. Strout
Why is scientific work in geohazard important - where does Geohazard fit in to oil business?
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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”
OnshoreVolcanism
Earthquakes
Slides/debris flows
Floods
Avalanches
OffshoreSlope instability
Earthquakes
Tsunamis
Shallow 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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HOST ORGANISATION
Norwegian Geotechnical Institute (NGI)
PARTNERS
University of Oslo (UiO)
NTNU
Geological Survey of Norway (NGU)
NORSAR
PARTNERS IN CENTRE OF EXCELLENCE
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TsunamiTsunami
Offshore geohazards
Gas hydrates or free gas
Mud volcano
Overpressure
Debris flow
Diapirism Doming
Underground blowout
t
Retrogressive
sliding
Gas chimney
Wave generation
Earth-quake
t
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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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Ormen Lange
Headwall 300 kmRun-out 800 kmVolume 5.600 km3
Area 34.000 km2
The Storegga Slide (8200 ybp)
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.
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• 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 – elements
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• 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
Geohazards study – Assessment
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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
1.5 2 2.5 3D e n sity (g /ccm )
200
150
100
50
0
20 40 60 80Po ro sity (% )
1 1.5 2 2.5V e lo city (km /s)
40 80 120Ga m m a (AP I)
900
850
800
750
700
650 Sed.type
Age(ka)
SITE 22
Seafloor
INO2
INO3
INO4
INO6
60
-15
,M
ove
d b
y S
tore
gg
a S
lide
13
0-6
01
50-
13
02
00
-
15
0
TW T (m s) D epth (m )
INO5?
Sa
mpl
es
N orm al m arine and/or d ista l g lacia l m arine sed im ents;c lay w ith som e s ilt, sand and occasional grave l.G enera lly fine gra ined
D eposits m ost like ly of un its O 1 and O 2, bu t m oved and d is turbed by the S toregga S lide ,
G lacia l debris flow deposits and g lacia l m arine deposits. G nera lly qu ite coarse gra ined.
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Defining critical geo-processes1D Basin model for Pressure-Temperature time history during
geological time Deposition rate
T=temperaturep=hydr. water pressureu=pore pressure=vertical soil stress’=eff. soil stress
dtdh
γ'tu
zu
c 2
2
v
z
Stress/pressure: p, u, ’
t
p u T
Sealevel change
h(t)
time
u ’
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Contributing processes/interactionGas hydrate melting caused by climate change after deglaciation
Geothermal gradient 50C/km
0
500
1000
1500
0 10 20 30 40 50 60
Horizontal distance, km
De
pth
be
low
se
ale
ve
l, m
Sea bed
Potential zone of GH melting
Sea level LGM
BGHSZ after sea level rise
BGHSZ at LGM sea level at -130m m
BGHZ after intrusionof warm atlantic surface water
Shelf edge
Sea level today
BGHSZ at LGM sea level at -130m m
BGHSZ after sea level rise
BGHZ after intrusionof warm atlantic surface water
Potential zone of GH melting
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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
0 2 4 6 8 10
0
100
200
300
400
500
600
700
Maximum Displacement, d (cms)
Dep
th b
elo
w m
udli
ne (
m) 0.30g
0.20g0.10g0.05g
0.01 0.10 1.00 10.00
0
100
200
300
400
500
600
700
Maximum Pore Pressure Ratioafter Seismic Event, u/s
vo (%)
Depth b
elo
w m
udlin
e (m
)
0.30g0.20g0.10g0.05g
Max. pore pressure ratio after event, %
Dep
th b
elom
mud
line,
m
Dep
th b
elom
mud
line,
m
Max. displacement, cm
0.30g0.20g0.
10g
0.0
5g
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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• + + +