Magnetotelluric survey applied to geothermal exploration: An example at Seokmo Island, Korea*
Tae Jong Lee 1 3 Nuree Han 2 Yoonho Song 11 Korea Institute of Geoscience and Mineral Resources (KIGAM), Gajeong-dong 30, Yuseong-gu, Daejeon 305-350, Korea.
2 Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151-742, Korea.
3 Corresponding author. Email: megi@kigam.re.kr
Exploration Geophysics 41(1) 61-68 https://doi.org/10.1071/EG10001
Submitted: 23 November 2009 Accepted: 14 December 2009 Published: 19 February 2010
Abstract
A magnetotelluric (MT) survey has been performed to delineate deeply extended fracture systems at the geothermal field in Seokmo Island, Korea. To assist interpretation of the MT data, geological surveying and well logging of existing wells were also performed. The surface geology of the island shows Cretaceous and Jurassic granite in the north and Precambrian schist in the south. The geothermal regime has been found along the boundary between the schist and Cretaceous granite. Because of the deep circulation along the fracture system, geothermal gradient of the target area exceeds 45°C/km, which is much higher than the average geothermal gradient in Korea. 2D and 3D inversions of MT data clearly showed a very conductive anomaly, which is interpreted as a fracture system bearing saline water that extends at least down to 1.5 km depth and is inclined eastwards. After drilling down to the depth of 1280 m, more than 4000 tons/day of geothermal water overflowed with temperature higher than 70°C. This water showed very similar chemical composition and temperature to those from another existing well, so that they can be considered to have the same origin; i.e. from the same fracture system. A new geothermal project for combined heat and power generation was launched in 2009 in Seokmo Island, based on the survey. Additional geophysical investigations including MT surveys to cover a wider area, seismic reflection surveys, borehole surveys, and well logging of more than 20 existing boreholes will be conducted.
Key words: fracture system, geothermal, magnetotelluric survey, Seokmo Island.
Acknowledgments
This work was supported by Basic Research Project of Korea Institute of Geoscience and Mineral Resources (KIGAM) and the Ministry of Land, Transport and Maritime Affairs through the project “Development of Marine Hydrothermal Mineral Deposits”. We thank the Geomagnetic Survey Institute (GSI) of Japan for providing the magnetotelluric monitoring data.
Gamble, T. D., Goubau, W. M., and Clarke, J., 1979, Magnetotelluric with remote reference: Geophysics 44, 53–68.
| Crossref | GoogleScholarGoogle Scholar |
Han, N., Nam, M. J., Kim, H. J., Lee, T. J., Song, Y., and Suh, J. H., 2008, Efficient three-dimensional inversion of magnetotelluric data using approximate sensitivities: Geophysical Journal International 175, 477–485.
| Crossref | GoogleScholarGoogle Scholar |
Lee, M. W., 1985, Jeju volcanic Island: Journal of Korean Earth Science Society 6, 49–53.
![](../../media/share/OpenURL_Image.gif)
Lee, S.-G., Kim, T.-K., Lee, J.-S., and Song, Y., 2006a, Rb-Sr Isotope geochemistry in Seokmodo granitoids and hot spring, Ganghwa: An application of Sr isotope for clarifying the source of hot spring: Journal of Petroleum Society of Korea 15, 60–71.
![](../../media/share/OpenURL_Image.gif)
Lee, T. J., Lee, S. K., Song, Y., and Uchida, T., 2006b, Use of Audio-band on the interpretation of magnetotelluric data: Mulli-Tamsa 9, 261–270.
![](../../media/share/OpenURL_Image.gif)
Park, D.-W., and Lee, C.-B., 2007, Characteristics of micro-crack orientations in Mesozoic granites and granite dyke rocks from Seokmo-do, Ganghwa-gun: Journal of Petroleum Society of Korea 16, 1–15.
![](../../media/share/OpenURL_Image.gif)
Uchida, T., 1993, Smooth 2-D inversion for magnetotelluric data based on statistical criterion ABIC: Journal of Geomagnetism and Geoelectricity 45, 841–898.
![](../../media/share/OpenURL_Image.gif)
1 *Part of this paper was presented at the 9th SEGJ International Symposium (2009).