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摘要: 開發地熱資源,尤其是深部干熱巖地熱資源,是加快能源結構轉型,順利實現“雙碳”目標的重要途徑。增強地熱系統經歷了50余年的發展,在深部地熱資源開采方面取得了豐富的研究成果和施工經驗。回顧增強地熱系統的發展歷程,總結熱儲特征、儲層改造以及示范項目的終止原因,分析商業化面臨的挑戰,探討未來的探索方向和發展機遇,能夠有效服務我國深部地熱資源開發和示范項目的建設。在經歷研究和開發階段后,增強地熱系統進入示范和商業化的飛速發展階段,截至2021年末,世界累計的增強地熱系統數量已達41個,累計發電裝機量為37.41 MW;儲層地質條件的復雜性和差異性以及現有改造技術對儲層原位地質環境的依賴性,難以形成“可復制”的熱儲改造模式,由此導致的熱儲質量差等問題是制約增強地熱系統發展的主要原因;建立典型的干熱巖增強地熱系統示范項目或探索基于采礦技術的增強地熱系統,突破熱儲改造對原位地質條件的依賴性,形成“可復制”的深部地熱資源開采體系,是增強地熱系統未來的發展方向,也是實現深部地熱資源大規模商業化的關鍵出路。Abstract: Exploiting geothermal resources, especially hot dry rock (HDR), is essential to reduce carbon emissions to build an acceptable energy structure. The enhanced geothermal system (EGS) for mining HDR has experienced more than 50 years since it was proposed in 1970, obtaining rich research results and construction experience. It is of great significance to review the EGS history, which includes discussing the project site selection and thermal storage stimulations, summarizing the reasons for the shutdown of demonstration projects, and indicating the key factors restricting EGS development. Based on this, the future development direction of EGS is clarified, which can help explore deep geothermal energy and construct associated demonstration projects in China. The overall development of EGS is divided into two stages, namely, the research and development stage before 2000 (a total of 14 EGS projects) and the demonstration and quasi-commercialization stage since 2000 with a rapid development speed (a total of 27 EGS projects). By the end of 2021, the cumulative number of EGS worldwide has increased to 41. However, the cumulative installed capacity of power generation only reaches 37.41 MW. EGS is still on the learning curve, resulting in a long way to go to realize the large-scale commercialization of HDR geothermal energy. The factors restricting the commercialization of EGS are the lack of policy support and capital investment, the limitations of technical difficulty, and the unpredictability of the geological condition of the thermal reservoir, which weakens EGS development and even causes its suspension or termination. Because of the complex geological environment of thermal reservoirs, the fracture network and associated reservoir quality induced by hydraulic stimulations are uncontrollable, causing the fractured quality of the thermal reservoir to be lower than its critical value. It results in numerous adverse problems in most EGS projects, including insufficient thermal reservoir volume, an unstable fracture network, associated heat exchange area, severe fluid loss, and induced unacceptable earthquakes. Thus, the fundamental reason for EGS’s inability to commercialize is that it is challenging to form a reproducible thermal reservoir stimulation model induced by the difference in thermal reservoir geological conditions and the dependence of the existing stimulation technologies on the in situ reservoir geological environment. Establishing the database of HDR and EGS plays an urgent role in EGS development by forming an accurate quantitative system of reservoir geological conditions to explore the relationship between geological conditions and reservoir reconstruction and then build a replicable thermal reservoir reconstruction technology. Focusing on new and demonstration stimulations for the thermal reservoir, such as the enhanced geothermal system based on caving technology (EGS-E), FORGE, and DEEPEGS projects, may provide an acceptable way to break through the dependence of thermal reservoir stimulation on in-situ geological conditions and form the “reproducible” deep-geothermal resource mining system to realize the large-scale commercialization of deep-geothermal resources.
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表 1 商業化EGS熱儲參數取值區間[3]
Table 1. Critical value of thermal reservoir parameters in a commercial EGS[3]
Parameters Critical value Parameters Critical value Flow rate/( L?s?1) 50?100 Thermal reservoir volume/m3 >2×108 Outlet temperature/℃ 150?200 Fluid resistance/(MPa?kg?1?s?1) <0.1 Effective heat exchange area/m2 >2×106 Water loss/% < 10 表 2 EGS項目發電裝機容量一覽表
Table 2. Total installed power generation capacity of EGS projects
Countries Projects Installed capacity
of power /MWCountries Projects Installed capacity
of power /MWUSA Fenton Hill 0.06 Germany Neustadt-Glewe 0.21 France Soultz 1.5 Germany Landau 3.6 Japan Hijiori 0.13 Germany Insheim 4.8* Australia Altheim 1.0 Germany Bruchsal 0.55 USA Desert Peak 1.7 Germany Gro? Sch?nebeck 1.0 Australia Habanero 1.0 Germany Unterhaching 3.36* El Salvador Berlin 6.0 USA Raft River 5.0* USA NW Geysers 3.5* UK Eden 4.0* Note:* denotes planned installed capacity, MW. 表 3 已終止的EGS項目概況一覽表
Table 3. Overview of the closed EGS projects
Countries Projects Lifespan Reasons for suspension or closure USA Fenton Hill 1972—1993 Insufficient heat reservoir scale; Severe fluid loss UK Rosemanowes 1976—1992 Severe fluid loss (above 70%); Earthquake (Mw 3.1) Germany Falkenberg 1977—1986 Low fluid temperature France Le Mayet 1978—1986 Low fluid temperature Japan Ogachi 1982—2002 Severe fluid loss (75%?90%) Sweden Fj?llbacka 1984—1995 Severe fluid loss (50%) Japan Hijiori 1981—1986 Severe fluid loss (70%); Sudden drop in fluid temperature Australia Hunter Valley 1999—2015 Lack of funds and policy support Switzerland Basel 1996—2006 Earthquake (Mw 3.4) USA Desert Peak 2008—2013 End of test USA Coso 2002—2012 Drilling fracturing accident Germany Bad Urach 2006—2008 Drilling fracturing accident Australia Habanero 2002—2013 Lack of funds and policy support Germany Horstberg 2003—2017 End of test Australia Paralana 2004—2014 Lack of funds and policy support Germany Landau 2007—2014 Earthquake USA Brady 2008—2015 End of test USA Southeast Geysers 2008—2009 Borehole collapse Switzerland St Gallen 2009—2014 Earthquake (Mw 3.4); Insufficient flow rate Korea Pohang 2015—2017 Earthquake (Mw 5.4) Note:Mw denotes the earthquake magnitude. 表 4 EGS項目微震或地震活動明細表
Table 4. Details of microseismic or earthquake activity in EGS projects`
Country Project Magnitude Lithology Country Project Magnitude Lithology UK Rosemanowes 3.1 Granite USA NW Geysers 2.8 Sandstone France Soultz 2.9 Granite Germany Insheim 2.4 Granite Switzerland Basel 3.4 Granite Germany Gro? Sch?nebeck 1.8 Sandstone USA Desert Peak 1.7 Granite Switzerland St Gallen 3.5 Carbonate USA Coso 2.8 Granite Germany Hannover 1.8 Sandstone Australia Habanero 3.7 Granite Korea Pohang 5.4 Granite El Salvador Berlin 4.4 Volcanic Finland Otaniemi 1.8 Granite Australia Paralana 2.6 Granite USA Milford 2.0 Granite Germany Landau 2.7 Granite -
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