利用反射震測探討宜蘭三星紅柴林地熱地下構造;Investigating underground structures of geothermal well sites by seismic reflection in the Ilan Plain, Taiwan

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Title:	利用反射震測探討宜蘭三星紅柴林地熱地下構造;Investigating underground structures of geothermal well sites by seismic reflection in the Ilan Plain, Taiwan
Authors:	黃家齊;chi,Huang chia
Contributors:	地球科學學系
Keywords:	蓋層;儲熱層
Date:	2015-07-27
Issue Date:	2015-09-23 11:29:35 (UTC+8)
Publisher:	國立中央大學
Abstract:	宜蘭平原位於台灣的東北端，在地形上為三角形的沖積盆地，面積約330平方公里，從地體構造，宜蘭平原位於菲律賓海板塊隱沒到歐亞板塊所造成的沖繩海槽的西南端，介於雪山山脈地質區(西及北方)與中央山脈地質區(南方)之間，並受到沖繩海槽弧後張裂(東方外海)的影響。宜蘭平原為第四紀河川沖積物堆積而成的三角洲平原，平原下方可能存在火成入侵，提供地熱的熱源。可能的地熱來源分為兩類，一為鄰近山區之變質岩熱源到達平原底下，如清水地熱來自中央山脈廬山層，礁溪溫泉則來自雪山山脈的四稜砂岩。二為沖繩海槽弧後張裂的火成活動進入平原底下深部，近岸的龜山島即為一明顯的火山島。因此，夾於中央山脈變質岩區與沖繩海槽火成岩區之間的宜蘭平原，地底下的地熱來源、熱源儲量及分布範圍，都需要進行有系統的全面性調查。本研究針對宜蘭平原地下構造進行一系列的地球物理調查，測區在羅東溪以西到泰雅橋的範圍(即三星-紅柴林地區)。以雙震盪車震源及中間展開384波道，48重合，在三星地區收集7條測線(每條約2至4公里)，探究宜蘭平原地下構造，仔細測繪三星紅柴林地區地下深部的地層，除了震測與地質鑽井資料比對，亦引用其他地球物理資料，如地震層析反演、空中磁測、大地電磁MT等資料，加以總和研判。震測研究結果發現，雪山山脈地質區的泰雅橋背斜向東延展，進入平原底下，背斜軸軸部向東傾斜12度，背斜兩翼傾角由西往東逐漸變小變平，從35度經8公里後減為10度，濁水斷層出泰雅橋後，在蘭陽溪南岸2至3公里處，往東延伸，濁水斷層分隔南邊之中央山脈地質區與北邊地雪山山脈地質區，斷層兩側岩性有差異，但地層幾何形貌類似，淺部沖積層明顯，厚度由山邊沿蘭陽溪增加，亦即基盤深度增加，至最深600m，基盤上部為乾溝層，厚度最厚可達1000公尺，岩性以板岩為主，劈理及裂隙發達，下覆為四陵砂岩，厚度800公尺，以石英砂岩為主。本研究認為此地區最適合開發地熱能源的地熱井址位在紅柴林營區北緣。 ;Investigating underground structures of geothermal well sites by seismic reflection in the Ilan Plain, Taiwan Abstract Due to the effect of back-arc spreading of Okinawa Trough, the Ilan plain in the northeastern corner of Taiwan potentially has geothermal resources. High geothermal temperature gradient up to 8oC/100m has been measured in the plain area. ‘Enhanced Geothermal System’ (EGS) is among the choices to develop this geothermal energy in Taiwan. The purpose of this study is to investigate geothermal drill sites by the high-resolution seismic reflection method. Two EnviroVibes with 384 channel Geode seismic recording system are used to study structures around planned geothermal well sites. Seven 2D seismic lines with the length 2 to 4 km are completed. The obtained seismic images are able to detect deep structures up to 2 sec (about 3km). The target is the SuLin formation(四稜砂岩) which is a crystallized sandstone layer in the HsueiShan Mountain Range. Many hot springs have been found around the outcrops of this layer in the mountain area. The seismic images indicate that the top alluvium layer has a thickness of 400m, beneath it is the KanKo formation(乾溝層) which is composed of fractured slate with visible reflection signals. The followed SuLin formation is at a depth of 1200m, but no obvious reflection images show up inside this layer. A sharp boundary between the KanKo and SuLin formation defines the target layer’s depth. Besides the layered structures, a large-scaled normal fault is also found in seismic profiles. The fault may provide fractures for the water to flow, which helps to develop an EGS system. However, high-resolution seismic reflection method can only image 1 to 2 km below the surface, it is necessary to compare with other geophysical methods such as magnetotelluric method (MT), seismic tomography and aero-magnetic survey to invest deeper structure. The result in SanShin HongChaiLin(三星紅柴林) shows three vital characteristics: low resistance, low velocity and high magnetic inductance, which implies this area is a high-potential geothermal zone. In conclusion, this study used seismic sections to derive the subsurface geological structure, which indicates the Kanko formation and the SuLin formation can be reliable cap and reservoir layers. Furthermore, combining with different geophysical methods, we are able to construct a proper geothermal model for the SanShin area. A good drill site has thus been decided at the northern corner of the HongChaiLin military camp.
Appears in Collections:	[Graduate Institute of Geophysics] Electronic Thesis & Dissertation

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