宜蘭清水地區二氧化碳增強型地熱系統之孔隙熱水模型研究

The Study of Porous TH Model of CO2-EGS in ChingHsui, ILan Assessment

本研究之目的為探討以超臨界二氧化碳（supercritical CO2）為取熱流體之二氧化碳增強型地熱系統（CO2-EGS）開發之可行性並預估其取熱產能以活化暫停開發之地熱井。為此，本研究以紅柴林2號井（HCL-2）與結元井（JY-1）為基礎，使用有限元素分析法建立了結合裂隙網路（fracture network）、孔隙熱傳與達西流（Darcy’s law）的孔隙-熱-水模型（porous-thermal-hydraulic model），並探討了儲集層於不同注入條件下的溫度變化趨勢及CO2-EGS之總產能。
由本研究可知當注入質量流率愈大，注入井底溫度變化大，生產井產出溫度愈高，使得EGS總產能愈高；大的注入質量流率可有效降低工作流體沿生產井流出時的溫降；然注入流體溫度對儲集層溫度分布幾乎沒有影響，生產井溫度對之亦較不敏感。在本研究中，CO2-EGS在注入質量流率為4 ton/hr與0.0005 ton/hr之條件比較發現，生產井口溫度增加約21.5%；溫降降低約16.96%，僅為約0.04%；總產能由23.6 kW增加到219 MW。而流量為4 ton/hr之比產能為571.4 kJ/kg，相較0.0005 ton/hr之比產能增加約11.8%。
未來本研究可結合更進一步之現地示蹤劑試驗數據做產能預估，評估以此二井為基礎建立CO2-EGS之產能與效益，可為活化已暫停開發之地熱井做出貢獻。

The re-utilization and activation of the abandon geothermal well was an economic concept for increasing the geothermal potential. The purpose of this study was to evaluate the feasibility of CO2 enhanced geothermal systems (CO2-EGS) based on the geothermal well HCL-2 and JY-1 and to estimate their capacity. A porous-fracture thermal-hydraulic model combined the fracture network, porous heat transfer model and Darcy's Law was established by finite element analysis. The temperature variation of the reservoir under different injected conditions and the total geothermal capacity of CO2-EGS are discussed.
The results show that the higher the mass flow rate of injection, the higher the outer temperature of the production well, the higher the total EGS capacity. The temperature difference of the production well decreased as the injected mass flow rate increased. The reservoir temperature distribution could be affected by the injected fluid temperature slightly. In this study, the temperature of the production wellhead of CO2-EGS increased about 21.5% when the injected mass flow rate was from 0.0005 ton/hr to 4 ton/hr. The specific capacity increased about 11.8%.
In future, this study can be combined with further in-situ tracer test data to estimate the capacity realistically, which can contribute to the activation of the abandon geothermal wells.