Insight into the Geothermal Structure in Chingshui, Ilan, Taiwan

Abstract

The Chingshui geothermal field is the largest known productive geothermal area in Taiwan. The purpose of this paper is to delineate this geothermal structure by integrating geophysical data and borehole information. The existence of a magma chamber in the shallow crust and shallow intrusive igneous rock results in a high heat flow and geothermal gradient; furthermore, the NE deep fault system within the meta-sandstones provides meteoric recharge from a higher elevation to artesianally drive the geothermal system. There is evidence that geothermal fluid deeply circulated within the fracture zone and was heated by a deeply located body of hot rock. The geothermal reservoir of the Chingshui geothermal field might be related to the fracture zone of the Chingshuihsi fault. It is bounded by the C-fault in the north and Xiaonanao fault in the south. Based on information obtained from geophysical interpretations and well logs, a 3-D geothermal conceptual model is constructed in this study. Further, the geothermal reservoir is confined to an area that is 260 m in width, N21°W, 1.5 km in length, and has an 80°dip toward the NE. A high-temperature zone is found in the SE region of the reservoir, which is about 500 m in length; this zone is located near the intersection of the Chingshuihsi and Xiaonanao faults. An area on the NE side of the high-temperature zone has been recommended for the drilling of production wells for future geothermal development.

South Ilan Plain High-Resolution 3-D S-Wave Velocity from Ambient Noise Tomography

“…9). The Chingshui location consistently exhibited a low S-wave velocity zone to a depth of 1.5 km, which corresponds well with its history of thermal explorations (Tong et al 2008). Further investigations are required to determine whether the thermal source extends to greater depths.…”

“…10), or just north of our fast anomaly zone (Tong et al 2008). Since our tomography results only have resolutions up to a depth of 1.5 km and the igneous dyke may not intrude to the surface, the sedimentary basement data remain the most prominent features in our study.…”

“…Since our tomography results only have resolutions up to a depth of 1.5 km and the igneous dyke may not intrude to the surface, the sedimentary basement data remain the most prominent features in our study. Tong et al (2008) conducted a magnetotelluric survey in Ilan and presented data indicating a geothermal reservoir that surfaced at Chingshui. To the north, however, the reservoir was covered by low resistivity cap rock.…”

“…It has been proposed that the observed EW trending magnetic anomalies crossing the mid-Ilan Plain may be caused by the acquired magnetisms of the upward magma body when cooled below the Curie temperature. These magma dikes are the likely heat sources (Tong et al 2008). …”

Silica Geothermometry Applications in the Taiwan Orogenic Belt

“…7a). This existing heat source is supported by other methods and results, the helium isotopic ratio of soil gases, seismic data, geomagnetic and magneto telluric data and borehole information (Yu and Tsai 1979;Yang et al 2005;Lan et al 2006;Tong et al 2008).…”