- 期刊
台灣東北部宜蘭平原淺部地熱水研究
A Study of Shallow Geothermal Resources in Ilan Plain, Northeastern Taiwan
摘要
台灣東北邊的宜蘭平原，面積約330平方公里，構造上位於沖繩海槽最西端的西邊，過去的研究皆認為沖繩海槽的張裂活動已進入平原內，為了解張裂活動所引發的熱流是否會對平原內淺部地層的溫度有所影響，以探討淺部地熱水的潛能，本研究於2003-2005年對平原上30口水井進行地溫測量，各水井量測深度最淺為27公尺，最深為178公尺，結果發現大部分地溫梯度都很低或呈現負值，顯示淺部地溫受地下水對流的影響，然而我們也發現平原南邊有6口井的地溫梯度超過正常值（3℃/100公尺），最高的龍德井為7.6℃/100公尺，高地溫梯度區域與高磁力異常區及地下水溶解氣顯示有地函物質來源區一致。另外，震測資料解釋此區基盤存在明顯斷層，地震發生也很密集，我們推測造成高地溫梯度的熱源應與磁力資料推演的火成岩脈入侵有關。假設各水井上部400公尺之地溫梯度如同淺部之觀測值，龍德井一帶在深度400公尺內即可發現50℃以上的地熱水，這將是目前台灣沖積平原上除溫泉區外地下水溫度達50℃的最淺區域。初步估計平原內第四紀地層35℃、40℃、45℃等溫線的範圍分別約95、53、21平方公里，厚度60-100公尺，若以孔隙率30%-60%計，40℃以上的地熱水儲量約為5100-10100×10^6立方公尺。
並列摘要
The Ilan plain (around 330 km^2) located in the northeastern Taiwan was considered an active area associated with the extending of Okinawa Trough opening. To evaluate the shallow geothermal potential, we have measured the thermal gradients (TGs) of 30 water wells from 27 to 178 m in depth in the plain from 2003 to 2005. The low (＜1.0℃/100 m) or negative TGs caused by the convection of groundwater are found in most of wells that are shallower than 50 m in depth. However, six wells with high TGs (up to 7.6℃/100 m) are identified in south of the plain where the location is consistent with the area of high magnetic anomaly, condense earthquakes, dissolved gas containing mantle material and fault zone in the basement. We suggest that the volcanic intrusion inferred by magnetic anomaly could be the heat source of the high geothermal and has increased the potential of shallow groundwater. The area of TGs great than 6.0℃/100 m is 36 km^2. This area is also the shallowest groundwater with temperature greater than 50℃ so far found in Taiwan alluvial plain without hot spring appearance. The area corresponding to groundwater with isotherms of 35℃, 40℃ and 45℃ are 95 km^2, 53 km^2, 21 km^2, respectively. Assuming the porosity is in the range of 0.3 to 0.6, and the TGs shallower than 400 m are approximately equal, we estimate the volume of groundwater with temperature higher than 40℃ is between 5,100×10^6 m^3 and 10,100×10^6 m^3.