臺灣宜蘭清水地熱區之應力狀態研究

Abstract

為了減緩對石化燃料過度的依賴以及減少二氧化碳的排放，開發新興能源不僅僅是最好的解決辦法，同時也是國際間的趨勢。在各式各樣新興能源當中，地熱發電是個發展較完備的技術。數十年來，宜蘭清水地熱地區以其豐富的地熱資源成名已久。一些初步的調查顯示在宜蘭清水的下方有著龐大的熱儲集層。因此，倘若地熱發電廠能在此處商轉，將對政府能源政策帶來正面的助益。

了解地層中導水裂隙是地熱發電廠以及增強型地熱系統(EGS)建構中關鍵的一環。而評估古應力與現地應力則能幫助我們判別應力場變化的狀態。有了現地應力與裂隙的資料之後，便可知道哪些裂隙會成為導水裂隙。清水地熱地區坐落於臺灣東北角，屬脊梁山脈西部板岩帶。此處位於板塊碰撞轉換到弧後張裂的過渡帶，應力狀態變化十分複雜，因此本研究將探討宜蘭清水地區之應力狀態。

我們使用地表斷層擦痕反演法以期估計應力演化狀態，此方法顯示出宜蘭清水一帶曾經歷至少三期不同的應力場。另一方面，我們透過IC-21號井所取得之岩心進行非彈性應變回復法(ASR)，以評估現地應力，其結果顯示：此區域正受到東北－西南向的擠壓與西北－東南向的拉張，呈現一走向滑移應力場，且此處應力比值極低，容易發生σ2與σ3互換之現象。此一結果與斷層擦痕反演法之最新一期結果一致，因此此結果足以代表宜蘭清水地熱地區之現地應力。In order to relieve the dependence on fossil fuels and reduce the production of carbonate-dioxide, the development of neo-energy is not only one of the best ways to work out but also the latest trends in the world. Among all the neo-energy sources, geothermal power plant is a well-developed technique. Chinshui geothermal district, Ilan, Taiwan has been known as one of famous geothermal districts for decades. Some preliminary research shows that there is a huge geothermal reservoir right below Chinshui, Ilan. It would be a great help to the energy policy if the efficient geothermal power plant could be set up here.

Understanding fluid conduit fractures is the key to develop geothermal power plants and further Enhanced Geothermal System (EGS). Assessing stress-state (both paleo& in-situ stress) helps out evaluating history evolution of stress states. Base on in-situ stress state in addition to fracture orientation, the passage or barrier of various fractures can be determined. Chinshui, Ilan locates in the western slate belt of Backbone Range, NE Taiwan. The variation of stress state here is quite complicated since the complex tectonic history of NE Taiwan resulted from collision to back-arc extension. In this work, multi methods were applied to find out the stress states around Chinshui, Ilan.

In order to evaluate paleo-stress states, analysis of heterogeneous fault-slipdata such as slickenside and quartz and calcite steps collected from outcrop along 10 km-long Chinshui area. Results show that at least three stages of stress state can be determined. On the other side, to know in-situ stress state, Anelastic Strain Recovery (ASR) method, a core-based method, was applied on the core retrieved form a latest drilling bore-hole of IC-21. Results show that NE-compression and NW-extension of strike-slip faulting stress regime with a low stress ratio. This result consisted with the youngest stage of stress state inferred from fault-slip analysis, impling that this strike-slip stress regime is the in-situ stress throughout the Chinshui geothermal district, Ilan.