Metamorphic geothermal reservoir characterisation-A case study in the Jinlun geothermal area, Taitung, Taiwan

There are more than one hundred hot spring outcrops around the island of Taiwan, which implies that Taiwan is rich in geothermal resources; however, no commercial geothermal power plants have been established since 1993, the year of the abandonment of a 3 MW geothermal plant in Chingshui. Situated at the oblique collision zone between Eurasia and Philippine Sea plates, most of Taiwan's hot springs are located in metamorphic terrain rather than volcanic areas. Previous study showed that geothermal resource is also rich in Jinlun area, whereas structural complexity and low permeability pose difficulties to geothermal exploitation. This paper aims to describe a geothermal conceptual model to facilitate the exploitation of the Jinlun geothermal field by integrating results from gravity, temperature surveys, surface geology, and information from recently conducted magnetotellurics survey and a new borehole. Results from the MT survey indicate a deep resistive structure down to 5 km depth. A zone of low resistivity (<5 ohm-m), which coincides with elevated temperatures observed in the borehole, could be attributed to thrust faulting. Based on 14C dating data, sources of geothermal brine could be connate water or meteoric water that travelled for a long distance. The main reservoir could be located at the fractured regions instead of porous strata.