以Play Fairway Analysis評估大屯火山群地熱潛能區位

Abstract

地熱能可永續利用，並且具有價格低廉及抵抗天災能力強等特性，為極具開發潛力的綠色能源。台灣位處太平洋火環帶，相關火山活動形成豐富地熱資源，其中位於北部的大屯火山群地熱蘊藏潛能更為優越。然而地熱探勘風險相當大，如何降低探勘成本、提高鑽井成功率是近年來所追求的目標。 Play Fairway Analysis為一種探勘方法，利用相關資料分析探勘要素之存在與否及有效程度，並製成風險區位圖，目的即量化、降低探勘鑽井的風險及不確定性。地熱資源形成須具備的要素：熱源、裂隙、流體，本研究針對其中的熱源及裂隙做討論，故蒐集大屯火山群可反映這兩個要素的研究資料，熱源圖層利用地溫梯度、地表溫泉溫度、氦同位素比值、溫泉露頭點、熱水換質帶及空中磁測所判釋之火成岩體資料；裂隙圖層利用斷層、微斷層分布及線型構造資料。將資料以ArcGIS軟體做處理，點資料以反距離權重法做內外插値，並且依據每個因子的重要程度，以層級分析法給予不同的權重，分別建立出熱源及裂隙的潛能圖層。其中，熱源準確性圖層則是為了確認點資料空間分布狀況，以資料點的影響半徑做為準確性劃分依據，修正部分無資料點位置的可信度。最終把熱源潛能圖層與裂隙潛能圖層疊合，以分數概念來量化潛能大小評估出潛能區位。 整合結果顯示，較有潛力之區位依序為小油坑、硫磺谷、馬槽、大油坑地區；但若考慮國家公園法之限制下，排除國家公園範圍後，較有潛力的區位則位於雙重溪下游及大埔兩處。再將流體酸鹼值所影響之發電成本考慮進去，則建議國家公園內以馬槽地區為首要開發位置，國家公園範圍外的地區則以雙重溪下游為目標。而這些潛能區位也與前人研究結論相符，顯示Play Fairway Analysis所分析出來的結果是具有可信度及可行性，故建議此方析法可應用在台灣其他亦具有地熱潛能的地區。

Geothermal resource is a sustainable and low-carbon emission energy. Previous studies revealed that the Tatun Volcano Group (TVG) has the most important potentials to develop the geothermal powers in Taiwan. However, it still has large inherent risk for investments due to uncertainty of reservoir locations and drilling sites. The risks of development can be lowered by using the Play Fairway Analysis (PFA) that integrates published data representing the composite risk segments in order to define the exploitation strategy. Heat and permeability are the most important two components for exploiting geothermal energy. This study collects and analyzes published geologic, geophysical and geochemical information to construct the conceptual models of heat and permeability in TVG. ArcGIS is used for data processing and modeling. The heat potential model is based on temperature gradient, temperature of hot spring, proximity to hot spring, hydrothermal alteration zones, helium isotope ratios and magmatic rocks from air magnetic survey. Whereas, the permeability potential model is relied on faults, fractures and lineation. Then, the parameters of these two potential models are weighted by the Analytical Hierarchy Process (AHP). Meanwhile, the uncertainty model is evaluated by the spatial accuracy of data. Integrated results show that the better places for geothermal developments are located at the Xiao-You-Keng, Liu-Huang-Ku, Ma-Tsao, and Da-You-Keng areas. Considering the Yangmingshan National Park where is forbidden for exploring and developing, the most suitable and ideal locations are in the downstream of Shuang-Chong River and Da-Pu areas. Thinking of the pH value of the fluids, the neutral fluid is more suitable for geothermal power generation. As a result, this study suggests that the Ma-Tsao area is the best site for geothermal developing. Outside of Yangmingshan National Park region, sets the downstream of Shuang-Chong River as the development target. Comparing the result with the previous study, the proposed areas for geothermal exploration are the same. In other words, it means that the result of the PFA is reliable and applicable. So, this method is applied not only in the TVG, but also other areas possessing geothermal potential in Taiwan.