| 摘要: | 地熱發電是台灣再生能源發展中重要的項目之一，其中位於宜蘭縣大同鄉的清水地熱案場為發展最早且相當成功的案例，目前已進入商業運轉階段。地熱開採通常伴隨地層中高溫岩體與流體的交互作用，因此本研究參考前人對清水地熱場址進行之相關研究，建立簡化地質模型與現地地質模型，考慮地層內部熱傳、水流及固體變形之間的交互作用，以多物理場模擬軟體COMSOL Multiphysics建立熱-水-力耦合數值模式。研究中首先採用簡化地質模型，以相對敏感度進行參數敏感度分析，並對模擬結果顯示具有高敏感度的參數做進一步討論，觀察不同參數設定下對熱-水-力耦合行為的影響。接著設計不同的抽注井間距與回注井回注深度，觀察不同設定對生產井溫度與壓力之影響，找到最適合的地熱井位配置。最後，採用現地地質模型進行生產回注模擬，觀察生產井溫度、水頭與地表面垂向位移變化情形。敏感度分析的結果顯示，熱容量與滲透率對溫度變化具有高敏感度，滲透率對水頭變化有高敏感度，而熱容量、熱膨脹係數、楊氏模數與泊松比則對應變變化有高敏感度。後續以上述參數探討抽注水過程中的行為差異可以發現，抽注水過程中引起的水-力耦合與熱-力耦合作用僅對岩體產生些微的應變量，對岩體中流體壓力造成的影響有限，因此幾乎不影響岩體中的流體流動與熱能傳遞。另外，抽注井間距評估結果顯示，當抽注井間距為200公尺左右時，生產溫度在20年內皆高於機組最低發電溫度，且同時擁有最低的降壓比。而回注深度評估結果顯示，當生產井生產深度為900公尺至1200公尺時，回注井回注深度600公尺至900公尺為最適合的回注方案。最後生產回注模擬結果顯示，在20年間地表面僅下降約0.0015公尺，顯示清水地熱案場在單一抽注情境下，生產過程不會造成顯著的地層抬升或下陷。;Geothermal power generation is a vital component of renewable energy development in Taiwan. Among the successful examples is the Chingshui geothermal power plant in Datong Township, Yilan County, which is one of the earliest developed and currently in commercial operation. Geothermal extraction typically involves the interaction between high-temperature rock and fluids within formation. This study references previous research on the Chingshui geothermal field to establish a simplified geological model and an in-situ geological model. It considers the interactions between heat transfer, fluid flow, and solid deformation within the formation, using the multiphysics simulation software COMSOL Multiphysics to create a coupled thermo-hydro-mechanical (THM) numerical model. In this research, parameter sensitivity analysis was conducted using relative sensitivity to identify parameters with high sensitivity, followed by a detailed discussion of the simulation results. The effects of different parameter settings on THM coupling behavior were observed. Finally, various configurations of production and injection well spacing and injection well depths were designed to evaluate their impacts on production well temperature and pressure, aiming to identify the optimal geothermal well configurations. Subsequently, the in-situ geological model was employed to perform production–injection simulations, observing changes in production well temperature, hydraulic head, and vertical displacement of the surface. The sensitivity analysis results indicate that heat capacity and permeability have high sensitivity to temperature changes, permeability has high sensitivity to hydraulic head changes, and heat capacity, thermal expansion coefficient, Young′s modulus, and Poisson′s ratio have high sensitivity to strain changes. Subsequent exploration of the behavior differences during the injection and production processes based on the above parameters revealed that during the injection and production processes, the HM and TM coupling only cause minor strain in the rock mass, which does not significantly affect pore pressure in the rock mass and thus scarcely influences fluid flow and heat transfer in the rock mass. Additionally, the assessment of production and injection well spacing indicates that a spacing of around 200 meters maintains the production temperature above the minimum power generation temperature for 20 years, while also achieving the lowest pressure drop ratio. The assessment of injection depth suggests that when the production well depth is between 900 meters and 1200 meters, the optimal injection well depth ranges from 600 meters to 900 meters. The production–injection simulation results indicate that, over a 20-year period, the surface displacement is approximately 0.0015 m, demonstrating that the geothermal production process does not result in significant ground uplift or subsidence.
Keywords: Thermo-hydro-mechanical coupling numerical simulation, Chingshui geothermal field, geological model, Parameter sensitivity analysis, Well spacing assessment, Injection depth assessment. |
