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Nantes, France

Vanneste M.,NGI Inc
74th EAGE Conference and Exhibition Incorporating SPE EUROPEC 2012 | Year: 2012

In this contribution, we review the current practice in submarine landslides research, in which a multidisciplinary approach is essential. These include, but are not limited to, geophysics, geology, geochemistry, geotechnics and geomechanics, slope stability simulations, landslide dynamics, consequence analysis (e.g., tsunami, impact, risk assessment). Following a brief introduction on the - typical - three-phase landslide development, we address a number of issues at stake (e.g., gas, hydrate, excess pore pressure) that should be addressed in more detail in future research activities within this field. These include in situ measurements, but also the advanced use of geophysical methods to derive soil properties in the shallow sub-surface. Finally, we highlight activities conducted to develop the Finneidfjord area (northern Norway) as a natural field laboratory for submarine landslide investigations. When it comes to smaller-scale landslides, high lateral and vertical resolution is paramount to understand such landslides, which still can have devastating consequences.

Josefsson S.,Umea University | Karlsson O.M.,IVL Swedish Environmental Reserach Institute Ltd | Karlsson O.M.,Uppsala University | Malmaeus J.M.,IVL Swedish Environmental Reserach Institute Ltd | And 4 more authors.
Chemosphere | Year: 2011

Water concentrations of PCDD/Fs, HCB, and non-ortho, mono-ortho, and non-dioxin-like PCBs were measured four times during 1year in a coastal area of the Baltic Sea, to investigate background levels and distribution behaviour. Sampling sites included two rivers, an estuary, and the sea. Particulate and apparently dissolved concentrations were determined using active sampling (filters+PUFs), while freely dissolved concentrations were determined using passive sampling (POM-samplers). The distribution between particulate+colloidal and freely dissolved phases, in the form of TOC-normalized distribution ratios (KTOC), was found to be near or at equilibrium. The observed KTOC were not significantly different between sampling sites or seasons. For PCDD/Fs, the concentrations were significantly correlated to suspended particulate matter (SPM), while no correlation to organic carbon (TOC) was observed. In the estuary and the sea, PCB concentrations were correlated to TOC. The sorption of various congeners to SPM and TOC appeared to be related to both hydrophobicity and 3D-structure. The PCDD/F concentration in the sea decreased to one third in May, likely connected to the increased vertical flux of particles during the spring bloom. © 2011 Elsevier Ltd.

Morgan E.C.,Tufts University | Vanneste M.,NGI Inc | Lecomte I.,NORSAR | Baise L.G.,Tufts University | And 2 more authors.
Geophysics | Year: 2012

Many previously proposed methods of estimating free gas saturation from seismic survey data rely on calibration to invasively collected, in situ measurements. Typically, such in situ measurements are used to parameterize or calibrate rock-physics models, which can then be applied to seismic data to achieve saturation estimates. We tested a technique for achieving estimates of the spatial distribution of gas saturation solely from shipboard seismic surveys. We estimated the quality factor from seismic reflection surveys using the spectral ratio method, and then inverted a mesoscopic-scale P-wave attenuation model to find the parameters that matched the modeled attenuation to our estimates of observed attenuation within the range of seismic frequencies. By using a genetic algorithm for this inversion, we not only searched efficiently for a global solution to the nonlinear set of equations that compose the model, but also constrain the search to a relatively broad set of realistic parameter values. Thus, our estimates do not rely on in situ measurements of these parameters, but on distributions of their possible values, many of which may be referenced from literature. We first tested this method at Blake Ridge, offshore North and South Carolina, where an approximately 400-m-deep gas-saturated zone underlies a field of methane hydrates. The extensive field work and subsequent studies at this site make it ideal for validating our method. We also demonstrated the applicability of our method to shallower deposits by presenting results from Finneidfjord, Norway, where the inversion of the P-wave attenuation model recognizes very small gas saturations. © 2012 Society of Exploration Geophysicists.

Pal S.,Gautam Buddha University | Kaynia A.M.,NGI Inc | Bhasin R.K.,NGI Inc | Paul D.K.,Indian Institute of Technology Roorkee
Rock Mechanics and Rock Engineering | Year: 2012

Stability analysis of Surabhi landslide in the Dehradun and Tehri districts of Uttaranchal located in Mussoorie India, has been simulated numerically using the distinct element method focusing on the weak zones (fracture). This is an active landslide on the main road toward the town centre, which was triggered after rainfall in July-August 1998. Understanding the behaviour of this landslide will be helpful for planning and implementing mitigation measures. The first stage of the study includes the total area of the landslide. The area identified as the zone of detachment is considered the most vulnerable part of the landslide. Ingress of water and increased pore pressures result in reduced mobilized effective frictional resistance, causing the top layer of the zone of detachment to start moving. The corresponding total volume of rock mass that is potentially unstable is estimated to 11.58 million m3. The second stage of this study includes a 2D model focussing only on the zone of detachment. The result of the analyses including both static and dynamic loading indicates that most of the total displacement observed in the slide model is due to the zone of detachment. The discontinuum modelling in the present study gives reasonable agreement with actual observations and has improved understanding of the stability of the slide slope. © 2011 Springer-Verlag.

Bjornara T.I.,University of Bergen | Bjornara T.I.,NGI Inc | Nordbotten J.M.,University of Bergen | Park J.,NGI Inc
Water Resources Research | Year: 2016

Models of reduced dimensionality have been found to be particularly attractive in simulating the fate of injected CO2 in supercritical state in the context of carbon capture and storage. This is motivated by the confluence of three aspects: the strong buoyant segregation of the lighter CO2 phase above water, the relatively long time scales associated with storage, and finally the large aspect ratios that characterize the geometry of typical storage aquifers. However, to date, these models have been confined to considering only the flow problem, as the coupling between reduced dimensionality models for flow and models for geomechanical response has previously not been developed. Herein, we develop a fully coupled, reduced dimension, model for multiphase flow and geomechanics. It is characterized by the aquifer(s) being of lower dimension(s), while the surrounding overburden and underburden being of full dimension. The model allows for general constitutive functions for fluid flow (relative permeability and capillary pressure) and uses the standard Biot coupling between the flow and mechanical equations. The coupled model retains all the simplicities of reduced-dimensional models for flow, including less stiff nonlinear systems of equations (since the upscaled constitutive functions are closer to linear), longer time steps (since the high grid resolution in the vertical direction can be avoided), and less degrees of freedom. We illustrate the applicability of the new coupled model through both a validation study and a practical computational example. © 2016. American Geophysical Union. All Rights Reserved.

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