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  • 學位論文

使用大地電磁法與電測資料建構宜蘭平原南部地熱模型

Geothermal conceptual model inferred from magnetotelluric and well-logging data in South Ilan Plain, Taiwan

指導教授 : 宋聖榮
共同指導教授 : 陳建志(Chien-Chih Chen)

摘要


臺灣位於菲律賓海板塊與歐亞板塊的交界處。菲律賓海板塊在台灣東北部隱沒至歐亞板塊下,形成一系列隱沒系統,此隱沒系統的末端即在臺灣東北處出露。透過地表熱特徵與高地溫梯度資料,我國政府將宜蘭平原南部列為地熱能源可探勘區域;然而2016年透過地球物理模型推測的探勘井,鑽取結果與預期結果有落差,前人認為可能源於此探勘區域特殊的地質背景。在傳統的火成岩地熱探勘區,利用大地電磁法所得的地球物理資料中,低電阻率數值指示含熱源的蓋層位置,然而宜蘭平原南側為變質岩區域,當初認為的低電阻區域可能有其他更合適的解釋。 故本研究將透過大地電磁資料與電測資料對比分析,以了解大地電磁法計算出的低電阻區域是否正確,若無誤,則此低電阻區域的成因為何?此成果對於往後變質岩區域中的電阻率資料判讀應該有更多可信的依據。 在初步的資料分析後,本研究認為大地電磁法的電阻率分布與電測資料趨勢大致相符,當初在低電阻率的判讀可能有其他更合理的解釋。透過更進一步的分析,得出此區域中的低電阻帶可能並非蓋層,由探勘井HCL1以及HCL2中的電測資料所示,研究區域的電阻率受孔隙率和飽和度控制,前提是無破裂帶的經過,若有破裂帶經過,可能使電阻率數值跳動劇烈,特徵不再那麼顯著。若後續解讀地熱概念模型時,除以孔隙率及飽和度的地層因子解讀外,因無法得知破裂帶與電阻率之相關性,建議配合震測等資料進行綜合判讀,找尋破裂帶可能位置,最後以此依據作出最合適的選址。

並列摘要


The Ilan Plain is located in the northeastern part of Taiwan. Geologically, it is the southwestward extension of the Okinawa Trough, which is a part of the subduction system with the Philippine Sea Plate being hidden under the Eurasian Plate. Based on the surface geothermal manifestations and higher temperature gradient, this area is a hot spot for the developments of geothermal resources in Taiwan. Two exploration wells based on the geophysical model, mainly through the magneto-telluric method (MT), were drilled in 2015-2016, but failed to get the expected result. The failed outcome suggested that the cap layer represented by the low-resistivity zone in the traditional resistivity model might be not used in metamorphic terranes. The aim of this study is to first reaffirm the previous MT results with well-logging and more MT data, then to examine any possible factors other than the clay cap that could create the resistivity anomaly, and finally to build a better geological model in this metamorphic terrane. After preliminary data analysis, it is believed that the resistivity distribution of the magneto-telluric method is roughly consistent with the trend of electrical measurement data. Through further analysis, it is believed that the low-resistivity zone in this area is not a cap layer. As shown by the well logging data in exploration wells HCL1 and HCL2, the resistivity of the study area is controlled by porosity and saturation, provided there is no passage of the fracture zone. If there is a fracture zone, the resistivity value may change drastically, and the characteristics are no longer so significant. In the subsequent interpretation of the geothermal conceptual model, in addition to the interpretation from porosity and saturation, since the correlation of the resistivity and the fracture zone cannot be found, it is recommended to cooperate with seismic data for comprehensive interpretation to find the possible location of best drilling sites.

參考文獻


Archie, G. E. (1942). The electrical resistivity log as an aid in determining some reservoir characteristics. Transactions of the AIME, 146(01), 54-62.
Asquith, G. B., Gibson, C. R. (1982). Basic well log analysis for geologists (Vol. 3): Amer Assn of Petroleum Geologists.
Avseth, P., Mukerji, T., Mavko, G. (2010). Quantitative seismic interpretation: Applying rock physics tools to reduce interpretation risk: Cambridge university press.
Bayrak, M., Serpen, Ü., İlkışık, O. (2011). Two-dimensional resistivity imaging in the Kızıldere geothermal field by MT and DC methods. Journal of Volcanology and Geothermal Research, 204(1-4), 1-11.
Blakeman, E. R. (1962). A Method of Analyzing Electrical Logs Recorded on a Logarithmic Scale. Journal of Petroleum Technology, 14(08), 844-850.

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