地層熱能單井抽取-儲存系統之熱流研析

Abstract

地層熱能儲存(aquifer thermal energy storage; ATES)系統為地熱利用技術之一，即在不同季節中，藉由水井灌注或抽取過程，將熱能儲蓄或抽出於含水層。單井抽取-儲存(single-well injection-extraction; SWIE)系統，其優點在於透過間歇性操作方式，以獲得或儲蓄熱能；此系統為ATES系統中最有效的使用方法之一。本研究目的在模擬受壓含水層與岩層所組成系統中，熱能抽取-儲蓄操作過程的溫度分佈情況，此含水層的上下皆為不透水、且具有不同物理特性和地層溫度梯度的岩層。本研究首先推導出一個運作SWIE系統之熱傳數學模式，此模式的熱傳過程包括含水層中沿著水平向和垂直向的熱傳導及強迫對流(forced convection)，而岩層內僅考慮垂直向的熱傳導。其次，應用Laplace轉換導出其無因次Laplace域的半解析解；然後，利用Crump方法數值逆轉Laplace域解，以獲得在時間域的數值解；最後，應用重疊原理(superposition principle)得到間歇性操作下的結果。接著引用文獻上的地質參數值，模擬SWIE系統中含水層和岩層的溫度分佈。由研究成果得知，含水層物理特性、地層溫度梯度、操作流量及間歇性操作和操作時間等因素，都會影響SWIE系統的溫度分佈。總而言之，本系統熱能抽取和儲蓄的效率受到流體通過水層與岩層交界處、井孔濾材間、熱傳導係數等影響。因此，系統操作之前，必須推估其操作效率。

Aquifer thermal energy storage (ATES) is a geothermal technology that stores/recovers thermal energy in/from aquifer storage at different seasons. The operation of a single-well injection-extraction (SWIE) system is an efficient measure of the ATES when adapting an intermittent operation such as sequentially injecting and storing waste heat in the ATES. In this thesis, a mathematical model is developed for describing the temperature distribution of the SWIE system based on the heat convection-conduction equation and the superposition principle. This system has a confined aquifer bounded by the impermeable rocks of different thermal properties and geothermal gradients along the depth. In the aquifer, the heat transfer processes include the horizontal conduction, vertical conduction, and forced convection along the water flow direction. In the rocks, only the vertical heat conduction is considered. A semi-analytical solution in dimensionless form for the temperature distribution is derived by the method of Laplace transform. The corresponding time-domain results are obtained by the modified Crump method. In addition, the results of intermittent operation are applied by using superposition principle. Field geothermal property data are applied to simulate the temperature distribution in a SWIE system. The predicted results indicate that the temperature distribution in the SWIE system is significantly affected by the thermal properties, geothermal gradient, injection/extraction flow rates, intermittent operation, and operating time. To conclude, the heat recovery and storage efficiency of the SWIE systems is mainly affected by the fluids through the interface between the aquifer and adjacent rocks, injection wellbores, and thermal conduction. Therefore, those efficiencies of the system must be determined prior to operation.