| Title | DEVELOPMENT OF EFFICIENT AND HIGH-RESOLUTION TEM METHOD FOR GEOTHERMAL EXPLORATION |
|---|---|
| Authors | K. Yoshimatsu, M. Tsuzuki, T. Mori, H. Watanabe, H. Ishikawa, T. Yamazaki |
| Year | 2018 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | geothermal exploration, SQUITEM, SQUID, TEM |
| Abstract | For the purpose of surveying geothermal resources, electromagnetic (EM) methods such as magnetotelluric (MT) and controlled-source audio-frequency MT (CSAMT) are widely used. However, the MT and CSAMT are disadvantaged in terms of a measurement efficiency in geothermal fields particularly located on mountainous areas such as Japanese geothermal fields, and in deep investigation, respectively. Therefore, JOGMEC has developed a SQUITEM system which is both high measurement efficiency and high resolution from shallow to deep section. The SQUITEM is a transient-EM (TEM) method using a super-conducting quantum interference device (SQUID) which is a high sensitivity magnetometer that has a wide bandwidth, a high dynamic range and offers high field sensitivity even at low frequency. SQUITEM was originally developed in order to investigate resistivity structures of shallow section for metal exploration. JOGMEC geothermal team focused on its high measurement efficiency and its high resolution, and considered whether it can be used for geothermal exploration. As a result of a field test of the original SQUITEM at Ogiri geothermal field in Kagoshima prefecture of Japan, we found that its measurement efficiency was good; however, its investigation depth was insufficient for geothermal explorations. Therefore, we constructed a new SQUITEM system for deep exploration more than 2 km depth. We tested the new SQUITEM system at the field near Yamagawa geothermal field in Kagoshima. By comparing with a previous MT survey at the same fields, we could show that the investigation depth of our new system was near 3 km. Moreover, since the investigation time is relatively short and therefore its cost is relatively low, we expect that our SQUITEM system can be a standard tool for geothermal exploration. |