| Title | Combining geophysical, isotopes and geological studies toward geothermal models at Hongchailin for geothermal power generation in NE Taiwan |
|---|---|
| Authors | J. Lee, G. Ho, C. Chen, H. Huang, C. Lin, S. Song, C. Chiang, Y. Lu, H. Hase, Y. Chan, C. Yang, Y. Chen, S. Chung |
| Year | 2023 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Geothermal geological model, Szeleng Sandstone, Hongchailin, Yilan, Taiwan |
| Abstract | In this study, we conduct a multi-disciplinary study, including geophysics, geochemistry, and geology, to reconstruct a geothermal geological model at the shallow 3 km level, for a project of potential geothermal power generation at the Hongchailin site in the Yilan plain of northeastern Taiwan. Our geophysical techniques include seismic imaging from natural earthquakes as well as ambient noise. Three seismic arrays deployed at different time periods in the past decade were used. We also incorporate geophysical imaging results from previous studies, in particular a series of seismic reflection profiles. Three magnetotelluric (MT) surveys have been conducted in three different periods. Three test holes were drilled around the Hongchailin site in 2016-2019. Logging and on-site measurements were conducted at increment depths, including rock types, P/T measurements, fractures analyses, geochemical analyses. Incorporating regional geological structures, geophysical subsurface imaging, we reconstruct geothermal geological models in line with detailed geological cross sections at the shallow 3 km level. We interpret a shallow geothermal reservoir within the massive quartz sandstone layers (Szeleng sandstone) at 1-2 km depth with the downhole temperature of 80-100°C. Geologically, the reservoir is located at the regional Songlo syncline and its south limb; and geophysically, it corresponds to a relatively low resistivity area. Isotope results show that the cool meteoric water came from nearby higher altitude mountain area, then flew through the Szeleng sandstone, which plunges 1-2 km depth below the Yilan plain. Hot fluid is interpreted to be derived from deeper heat source interpreted from seismicity data, which then upflows along a N-S trending vertical faults system. Dronebased thermal imagery confirmed the presence of hotter areas at surface. In addition, two E-W trending major faults, identified by the seismic reflection profiles, seem to act as hydrothermal fluid barriers to confine the hot fluid within the reservoir area. |