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Seismic investigations in the Brunswick No. 6 area, Canada – Imaging and heterogeneity
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Brunswick No. 6 area, which is located in the Bathurst Mining Camp, New Brunswick, Canada, is the focus of this thesis. Almost a decade ago, in order to improve the understanding of the crustal structures and explore for new mineral deposits at depth, three 2D seismic profiles totaling about 30 km and 3D seismic data covering an area of about 38 km2 were acquired from the study area. Petrophysical properties including compressional-wave velocity and density were also measured in two deep boreholes in the area. These data were recovered and reanalyzed, and the improved seismic images interpreted as the main part of this PhD thesis.

A prestack DMO and poststack migration algorithm was considered for processing both 2D and 3D data. Processing of 2D data revealed shallow and deep reflections, which correlate well with surface geology. Steeply-dipping reflections, some of which could host mineral deposits, were imaged down to a depth of 6-7 km. Processing of 3D data showed similar results to the processed 2D profiles. Nevertheless, the non-orthogonal nature of the 3D survey, combined with irregular distribution of offsets, azimuths and trace midpoints, caused a severe acquisition footprint masking reflections in the DMO-corrected unmigrated stacked cube. An FK-dip filter in the wavenumber domain was designed to reduce the effects of the acquisition footprint.

To better understand wave propagation and scattering effects, calculated acoustic impedance log from the available borehole data was used to estimate vertical scale length using a von Karman autocorrelation function. 2D synthetic models representative of heterogeneity in the area were generated accounting for the estimated scale length. Numerical modeling was used to study the scattering effects on the synthetic models, where some predefined targets were superimposed in the provided 2D heterogeneous medium. The effects of variable source frequency, longer horizontal scale length and petrophysical fluctuations of heterogeneous medium were also investigated. The modeling results indicate that, in the presence of large horizontal, but small vertical scale lengths (structural anisotropy), the identification of mineral deposits is possible in the unmigrated stacked sections, but can be challenging in the migrated sections.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 73 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1013
Keyword [en]
Brunswick No. 6, Mineral deposits, 2D and 3D reflection seismic, Acquisition footprint, Scale length, Heterogeneity, Numerical modeling
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
URN: urn:nbn:se:uu:diva-190479ISBN: 978-91-554-8578-8 (print)OAI: oai:DiVA.org:uu-190479DiVA: diva2:583655
Public defence
2013-03-01, Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2013-02-08 Created: 2013-01-08 Last updated: 2013-04-02
List of papers
1. Crustal-scale reflection seismic investigations in the Bathurst Mining Camp, New Brunswick, Canada
Open this publication in new window or tab >>Crustal-scale reflection seismic investigations in the Bathurst Mining Camp, New Brunswick, Canada
2011 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 506, no 1-4, 55-72 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2011
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-165237 (URN)10.1016/j.tecto.2011.04.011 (DOI)
Available from: 2012-01-09 Created: 2012-01-04 Last updated: 2017-12-08Bibliographically approved
2. 3D imaging challenges in steeply dipping mining structures: New lights on acquisition geometry and processing from the Brunswick no. 6 seismic data, Canada
Open this publication in new window or tab >>3D imaging challenges in steeply dipping mining structures: New lights on acquisition geometry and processing from the Brunswick no. 6 seismic data, Canada
2012 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 77, no 5, WC109-WC122 p.Article in journal (Refereed) Published
Abstract [en]

We have analyzed and processed a 38-km(2) nonorthogonal 3D surface reflection seismic data in the Brunswick no. 6 area to better understand the effect of acquisition geometry on the resultant image and to provide 3D information about the main geologic structures hosting the mineralization. The 3D data were processed using a conventional prestack dip moveout (DMO) and poststack migration algorithm with special focus on refraction static corrections, velocity analysis, and DMO corrections that are important for the data recorded in crystalline environment. However, the nonorthogonal nature of the 3D data combined with its narrow-azimuth, irregular offset distributions, and 2D nature of midpoint distribution in common depth point bins resulted in a lower quality seismic image than those observed on a series of 2D seismic profiles collected in the area prior to the 3D data acquisition. 2D wavenumber spectrum of the data suggests acquisition footprint associated with the data. Most of the noise associated with the acquisition footprint manifested itself as short-length, high-amplitude shallow reflections but largely were attenuated using a dip filter running in the wavenumber domain. Various bin size and geometries were tested, and the best result was obtained using rectangular bins aligned in the orientation of the shot lines. The processing results indicated that the highly prospective and mineralized Brunswick horizon is part of a continuous reflective package that could guide future deep mineral exploration in this mining camp.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-183770 (URN)10.1190/GEO2011-0475.1 (DOI)000309077200044 ()
Available from: 2012-11-02 Created: 2012-11-01 Last updated: 2017-12-07Bibliographically approved
3. Scaling behavior and the effects of heterogeneity on shallow seismic imaging of mineral deposits: a case study from Brunswick No. 6 mining area, Canada
Open this publication in new window or tab >>Scaling behavior and the effects of heterogeneity on shallow seismic imaging of mineral deposits: a case study from Brunswick No. 6 mining area, Canada
Show others...
2013 (English)In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 90, 1-18 p.Article in journal (Refereed) Published
Abstract [en]

We have studied the scaling behavior of compressional-wave velocity and density logs from an exploration borehole that extends down to about 700 m depth in the Brunswick No. 6 mining area, Bathurst Mining Camp, Canada. Using statistical methods, vertical and horizontal scale lengths of heterogeneity were estimated. Vertical scale length estimates from the velocity, density and calculated acoustic impedance are 14 m, 33 m, and about 20 m, respectively. Although the estimated scale length for the acoustic impedance implies a weak scattering environment, elastic finite difference modeling of seismic wave propagation in 2D heterogeneous media demonstrates that even this weak scattering medium can mask seismic signals from small, but yet economically feasible, massive sulphide deposits. Further analysis of the synthetic seismic data suggests that in the presence of heterogeneity, lenticular-shaped targets may only exhibit incomplete diffraction signals whereby the down-dip tails of these diffractions are mainly visible on the stacked sections. Therefore, identification of orebody generated diffractions is much easier on the unmigrated stacked sections than on migrated stacked sections. The numerical seismic modeling in 2D heterogeneous media indicates that in the presence of large horizontal, but small vertical scale lengths (structural anisotropy), identification of massive sulphide deposits is possible, but their delineation at depth requires detailed velocity modeling and processing algorithms which can handle the anisotropy.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
crystalline rock, scattering, heterogeneity, scaling, modeling
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-189088 (URN)10.1016/j.jappgeo.2012.12.003 (DOI)000316167700001 ()
Available from: 2012-12-23 Created: 2012-12-23 Last updated: 2017-12-06Bibliographically approved

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