Magnetotelluric imaging of anisotropic crust near Fort McMurray, Alberta: implications for engineered geothermal system development
Viability for the development of an engineered geothermal system (EGS) in the oilsands region near Fort McMurray, Alberta, is investigated by studying the structure of the Precambrian basement rocks with magnetotellurics (MT). MT data were collected at 94 broad-band stations on two east–west profile...
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Online Access: | http://hdl.handle.net/10044/1/42819 https://doi.org/10.1093/gji/ggw089 |
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ftimperialcol:oai:spiral.imperial.ac.uk:10044/1/42819 2023-05-15T16:17:37+02:00 Magnetotelluric imaging of anisotropic crust near Fort McMurray, Alberta: implications for engineered geothermal system development Liddell, M Unsworth, MJ Pek, J 2016-03-01 http://hdl.handle.net/10044/1/42819 https://doi.org/10.1093/gji/ggw089 unknown Oxford University Press (OUP) Geophysical Journal International The Authors 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society 1381 1365 Geochemistry & Geophysics 0404 Geophysics 0403 Geology 0909 Geomatic Engineering Journal Article 2016 ftimperialcol https://doi.org/10.1093/gji/ggw089 2018-09-16T05:57:44Z Viability for the development of an engineered geothermal system (EGS) in the oilsands region near Fort McMurray, Alberta, is investigated by studying the structure of the Precambrian basement rocks with magnetotellurics (MT). MT data were collected at 94 broad-band stations on two east–west profiles. Apparent resistivity and phase data showed little variation along each profile. The short period MT data detected a 1-D resistivity structure that could be identified as the shallow sedimentary basin underlain by crystalline basement rocks to a depth of 4–5 km. At lower frequencies a strong directional dependence, large phase splits, and regions of out-of-quadrant (OOQ) phase were detected. 2-D isotropic inversions of these data failed to produce a realistic resistivity model. A detailed dimensionality analysis found links between large phase tensor skews (∼15°), azimuths, OOQ phases and tensor decomposition strike angles at periods greater than 1 s. Low magnitude induction vectors, as well as uniformity of phase splits and phase tensor character between the northern and southern profiles imply that a 3-D analysis is not necessary or appropriate. Therefore, 2-D anisotropic forward modelling was used to generate a resistivity model to interpret the MT data. The preferred model was based on geological observations of outcropping anisotropic mylonitic basement rocks of the Charles Lake shear zone, 150 km to the north, linked to the study area by aeromagnetic and core sample data. This model fits all four impedance tensor elements with an rms misfit of 2.82 on the southern profile, and 3.3 on the northern. The conductive phase causing the anisotropy is interpreted to be interconnected graphite films within the metamorphic basement rocks. Characterizing the anisotropy is important for understanding how artificial fractures, necessary for EGS development, would form. Features of MT data commonly interpreted to be 3-D (e.g. out of OOQ phase and large phase tensor skew) are shown to be interpretable with this 2-D anisotropic model. Article in Journal/Newspaper Fort McMurray Imperial College London: Spiral Fort McMurray Geophysical Journal International 205 3 1365 1381 |
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Imperial College London: Spiral |
op_collection_id |
ftimperialcol |
language |
unknown |
topic |
Geochemistry & Geophysics 0404 Geophysics 0403 Geology 0909 Geomatic Engineering |
spellingShingle |
Geochemistry & Geophysics 0404 Geophysics 0403 Geology 0909 Geomatic Engineering Liddell, M Unsworth, MJ Pek, J Magnetotelluric imaging of anisotropic crust near Fort McMurray, Alberta: implications for engineered geothermal system development |
topic_facet |
Geochemistry & Geophysics 0404 Geophysics 0403 Geology 0909 Geomatic Engineering |
description |
Viability for the development of an engineered geothermal system (EGS) in the oilsands region near Fort McMurray, Alberta, is investigated by studying the structure of the Precambrian basement rocks with magnetotellurics (MT). MT data were collected at 94 broad-band stations on two east–west profiles. Apparent resistivity and phase data showed little variation along each profile. The short period MT data detected a 1-D resistivity structure that could be identified as the shallow sedimentary basin underlain by crystalline basement rocks to a depth of 4–5 km. At lower frequencies a strong directional dependence, large phase splits, and regions of out-of-quadrant (OOQ) phase were detected. 2-D isotropic inversions of these data failed to produce a realistic resistivity model. A detailed dimensionality analysis found links between large phase tensor skews (∼15°), azimuths, OOQ phases and tensor decomposition strike angles at periods greater than 1 s. Low magnitude induction vectors, as well as uniformity of phase splits and phase tensor character between the northern and southern profiles imply that a 3-D analysis is not necessary or appropriate. Therefore, 2-D anisotropic forward modelling was used to generate a resistivity model to interpret the MT data. The preferred model was based on geological observations of outcropping anisotropic mylonitic basement rocks of the Charles Lake shear zone, 150 km to the north, linked to the study area by aeromagnetic and core sample data. This model fits all four impedance tensor elements with an rms misfit of 2.82 on the southern profile, and 3.3 on the northern. The conductive phase causing the anisotropy is interpreted to be interconnected graphite films within the metamorphic basement rocks. Characterizing the anisotropy is important for understanding how artificial fractures, necessary for EGS development, would form. Features of MT data commonly interpreted to be 3-D (e.g. out of OOQ phase and large phase tensor skew) are shown to be interpretable with this 2-D anisotropic model. |
format |
Article in Journal/Newspaper |
author |
Liddell, M Unsworth, MJ Pek, J |
author_facet |
Liddell, M Unsworth, MJ Pek, J |
author_sort |
Liddell, M |
title |
Magnetotelluric imaging of anisotropic crust near Fort McMurray, Alberta: implications for engineered geothermal system development |
title_short |
Magnetotelluric imaging of anisotropic crust near Fort McMurray, Alberta: implications for engineered geothermal system development |
title_full |
Magnetotelluric imaging of anisotropic crust near Fort McMurray, Alberta: implications for engineered geothermal system development |
title_fullStr |
Magnetotelluric imaging of anisotropic crust near Fort McMurray, Alberta: implications for engineered geothermal system development |
title_full_unstemmed |
Magnetotelluric imaging of anisotropic crust near Fort McMurray, Alberta: implications for engineered geothermal system development |
title_sort |
magnetotelluric imaging of anisotropic crust near fort mcmurray, alberta: implications for engineered geothermal system development |
publisher |
Oxford University Press (OUP) |
publishDate |
2016 |
url |
http://hdl.handle.net/10044/1/42819 https://doi.org/10.1093/gji/ggw089 |
geographic |
Fort McMurray |
geographic_facet |
Fort McMurray |
genre |
Fort McMurray |
genre_facet |
Fort McMurray |
op_source |
1381 1365 |
op_relation |
Geophysical Journal International |
op_rights |
The Authors 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society |
op_doi |
https://doi.org/10.1093/gji/ggw089 |
container_title |
Geophysical Journal International |
container_volume |
205 |
container_issue |
3 |
container_start_page |
1365 |
op_container_end_page |
1381 |
_version_ |
1766003516642426880 |