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Kantia P.,Geofcon | Heikkinen E.,Pöyry | Cosma C.,Vibrometric Canada Ltd. | Enescu N.,Vibrometric Canada Ltd. | And 2 more authors.
47th US Rock Mechanics / Geomechanics Symposium 2013 | Year: 2013

Posiva in Finland and SKB in Sweden are preparing for spent nuclear fuel disposal in crystalline bedrock. Disposal relies on the geological KBS-3 multiple barrier concept. In this concept surrounding rock mass is considered as one barrier preventing radionuclide transportation to the biosphere. Excavation of disposal tunnels will be conducted using a drill and blast (D&B) tunneling method. Blasting and stress field redistribution unavoidably causes an excavation damaged zone (EDZ) which needed to be investigated. This study concentrates on characterization methods revealing the properties and significance of the EDZ. Non-destructive testing (NDT) methods were advised to enhance coverage and efficiency of investigations. Chosen study methods were seismic reflection and tomography, electrical resistivity tomography, ground penetrating radar investigations, borehole imaging, hydraulic measurements and laboratory analysis of rock samples. Results obtained from different scales and the chosen methods were compared. Analysis led to observation of discontinuous character and varying thickness of the EDZ. Research indicates a fairly thin, 5-30 cm thick EDZ layer on rock surfaces. Excavation and stress redistribution induced fractures might contribute to hydraulic flow close to the tunnel perimeter. Locating and mapping of these potential hydraulic paths can be performed with high resolution geophysical NDT methods. Copyright 2013 ARMA, American Rock Mechanics Association.

Wood G.,Cameco Corporation | O'Dowd C.,Cameco Corporation | Cosma C.,Vibrometric Canada Ltd | Enescu N.,Vibrometric Canada Ltd
Geophysics | Year: 2012

The Millennium uranium deposit is located within the Athabasca Basin, in northern Saskatchewan, Canada. The deposit is hosted within moderately dipping Paleoproterozoic gneisses that are unconformably overlain by more than 500 m of flat lying, porous Paleoproterozoic to late Mesoproterozoic Athabasca Group sandstones. The deposit is associated with the sandstone-basement unconformity, post-Athabasca structure, and hydrothermal alteration. These features combine to create a complex 3D hydrogeologic setting that presents challenges with respect to mine development, production, and safety. In 2007, as part of a prefeasibility study for potential mine development, a seismic program consisting of a 3D surface survey, vertical seismic profiling, moving source profiling, and side-scan surveys was undertaken to map the complex geology. The geometry and resolution of these different seismic surveys allowed for direct imaging of the geologic targets of interest, regardless of orientation and size. After integration with drill-defined geology, the program successfully imaged the location and character of the unconformity, the post-Athabasca structural setting at camp and deposit scales, and the alteration around the deposit. This information increased the understanding of geotechnical aspects of the geology hosting the deposit, and is currently being used to help minimize risk and costs associated with mine development. Seismic surveys are now viewed as an integral part of risk reduction associated with mining in the Athabasca Basin. © 2012 Society of Exploration Geophysicists.

Cosma C.,Vibrometric Canada Ltd. | Balu L.,Vibrometric Canada Ltd. | Enescu N.,Vibrometric Canada Ltd.
Geophysics | Year: 2010

The common characteristic of the seismic methods involving downhole measurements is the difficulty of designing surveys able to image the subsurface space evenly. Migration schemes for these layouts are sensitive to reconstruction artifacts. The defining property of the image point (IP) transform is its ability to accumulate amplitudes of curved reflection events appearing in time-distance profiles into approximately discoidal (or spherical in three dimensions) vicinities in the IP domain. Due to the reflected wavefields collapsing into such vicinities in the IP domain, the emphasizing of the reflectors consists of enhancing regions with higher amounts of accumulated amplitude. True-dip filtering can also easily be performed, even for reflectors appearing in the time-distance profiles as curved events due to their dip, source offset or variable velocity field. Reflecting interfaces aredefined as sets of linked piecewise planar-reflector elements rather than as collections of point diffractors. True reflectors fitting this description are enhanced by the IP transform while diffraction patterns, events produced by other wave types, multiples, and noise of any kind, tend to be suppressed. The inverse transform leads to filtered versions of time-distance profiles. An alternative to performing the inverse transform back to the original time-distance representation is computing 2D/3D migrated images directly from the transformed IP space. Although the 3D migration by IP transform is applicable to any seismic survey geometry, we focused on procedures for enhancing prestack migrated images obtained by sparse multioffset, multiazimuth vertical seismic profiling (VSP) surveys as typically performed for mining site characterization and mineral exploration. The real data used were collected within an extensive mining seismic investigation program performed in Canada. © 2010 Society of Exploration Geophysicists.

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