大地電磁影像加強了解地熱構造:宜蘭清水地熱案例

Magnetotelluric Imaging Improves Understanding of Geothermal System: Case in Chingshui Geothermal Area, Northeastern Taiwan

英萬(Irwan)

指導教授 ： 陳洲生

國立中央大學/地球科學學院/地球物理研究所/碩士(2012年)

摘要

清水地熱是台灣發展最完整之地熱區，其熱源來自入侵淺部(~2km)之火成岩體造成高地熱流與地溫梯度，變質砂岩中一些東北向深部斷層系統提供天水深循環(3He/4He比值)之熱水通路。本研究再處理原資料，包括二維模擬及逆推，結果顯示(圖5.2) 沿清水斷之低電阻異常(C1 與 C2)
是清水地熱儲集層，其上之粘土化礦物屬地熱蓋層。清水斷層是熱水上升至地表之主要通道，此外，高電阻多裂隙(微震密集)圍岩R2以及東側鄰近之火成入侵體R1屬清水地熱熱源。
本研究最重要之發現是在淺部C1與C2 5Km下存在深部區域性低電
阻異常C3，兩者彼此經由清水斷層相連，C3可能是未來清水地熱發展加強型地熱主要目標。大地電磁併合地質、地物以及地化確實加強了解清 水地熱構造。

關鍵字

清水地熱 ； 地熱系統 ； 大地電磁法

並列摘要

The well known geothermal field in Taiwan is Chingshui geothermal area (CGA). The existence of a shallow (~2km) intrusive igneous rock results in a high heat flow and geothermal gradient. The NE deep fault system within the meta-sandstones provides meteoric recharge from a higher elevation to artesianally drive the geothermal system. This study reprocess the 2D modeling and inversion of CGA MT data. The result (Fig. 5.2) shows that anomalously conductive (3-100 ?m) zones, C1 and C2, obtained along the Chingshui fault may represent the geothermal reservoir in this area and the cap formed by clay mineral on top of it. Chingshui fault may act as a main conduit for fluid migration toward the surface. Meanwhile, the high resistivity (300-1000 ?m) host rock, with high temperature gradient and fracture dominated (seismicity indicated) (R2), together with the magma intrusion nearby (R1) represent the possible heat source of CGA.
The most interesting feature of this study is the finding of another deeper conductor (C3). C3 conductor is at about 5 km beneath the shallow conductor C1 and C2. All conductors (C1, C2 and C3) in CGA are connected each other by Chingshui fault. However, C3 conductor is most probably the highest potential for enhanced or engineered geothermal system (EGS) in CGA as it owns regional, rather local, enhanced hear and fluid. MT sounding technique, by joint interpretation with geology, geophysical and geochemical information does improve understanding of the geothermal system.

並列關鍵字

magnetotelluric ； Chingshui geothermal area. ； geothermal system

參考文獻

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