Assessment - Prevention - Mitigation Presented by James M. Strout Why is scientific work in geohazard important - where does Geohazard fit in to oil business?

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 GEOHAZARDS Assessment, 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.

HOST ORGANISATION Norwegian Geotechnical Institute (NGI) PARTNERS University of Oslo (UiO) NTNU Geological Survey of Norway (NGU) NORSAR PARTNERS IN CENTRE OF EXCELLENCE

Tsunami Offshore geohazards Gas hydrates or free gas Mud volcano Overpressure Debris flow Diapirism Doming Underground blowout Retrogressive sliding Gas chimney Wave generation Earth- quake

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

Ormen Lange Headwall 300 km Run-out  800 km Volume  km 3 Area  km 2 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.

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

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

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 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.

Thank your for your attention!

Overheads illustrating each element of a geohazard study

Geophysical investigation Improved imaging techniques

In situ conditions and material properties Correlation of geological, geotechnical, and geophysical parameters

Defining critical geo-processes 1D Basin model for Pressure-Temperature time history during geological time Deposition rate T=temperature p=hydr. water pressure u=pore pressure  =vertical soil stress  ’=eff. soil stress z Stress/pressure: p,  u,  ’ tt p u  T Sealevel change h(t) time uu ’’

Contributing processes/interaction Gas hydrate melting caused by climate change after deglaciation Geothermal gradient 50  C/km BGHSZ at LGM sea level at -130m m BGHSZ after sea level rise BGHZ after intrusion of warm atlantic surface water Potential zone of GH melting

Failure mechanism Retrogressive 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

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 Max. pore pressure ratio after event, % Depth belom mudline, m Max. displacement, cm 0.30g 0.20g 0.1 0g 0.0 5g

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

Evaluate consequences Tsunami modelling and prediction

Evaluating probabilities Variability/incompleteness of data Modelling errors Recurrence of triggering mechanisms Presence of necessary conditions + + +