| Title | Geothermal conceptual model inferred from magnetotelluric and well-logging data in South Ilan Plain, Taiwan |
|---|---|
| Authors | J. Lin, S. Song and C. Chen |
| Year | 2019 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | magnetotelluric, well-logging |
| Abstract | The Ilan Plain is located in the northeastern part of Taiwan. Geologically, it is the southwestward extension of the Okinawa Trough, which is a part of the subduction system with the Philippine Sea Plate being hidden under the Eurasian Plate. Based on the surface geothermal manifestations and higher temperature gradient, this area is a hot spot for the developments of geothermal resources in Taiwan. An exploration well based on the geophysical model, mainly through the magneto-telluric method, was drilled in 2016 but failed to get the expected result. The failed outcome suggests that the cap layer represented by the low-resistivity zone in the traditional resistivity model may be unsuitable for metamorphic areas. The aim of this study is to first reaffirm the previous MT results with well-logging data and additional MT data, then examine any other possible factors other than the clay cap that could create the resistivity anomaly, and finally build a better geological model in this metamorphic terrane. Our preliminary analysis confirms the MT outcome and proposes three possible scenarios of resistivity variation for better modeling. One interpretation is that the low resistivity zone may be caused by a sandstone layer containing plentiful iron sulfide, e.g. pyrite, instead of a clay cap. Mixing with different resistivity components from the groundwater and the amount of carboniferous materials in the formation are also possibly affecting the resistivity. Further work needs to be done to identify the most likely factors to explain the resistivity disparity. |