增强型地热系统关键技术研究现状及发展趋势

Research status and development trend of key technologies for an enhanced geothermal system

增强型地热系统(EGS)是开发干热岩型地热资源的主要手段,但其目前存在高温作用下人工压裂缝网不合理、多尺度多场耦合规律不明、井内闪蒸流动造成采热效率低下、地热流体热电转换效率低等关键问题,不利于地热资源的大规模商业化开发。围绕上述重大瓶颈问题,针对EGS开采干热岩型地热资源涉及的4大关键技术,系统梳理和分析了各项技术的研究进展及发展趋势。主要内容包括:①在干热岩储层人工压裂技术方面,详述了储层改造方法、人工缝网形成机制和裂缝扩展预测模型等方面的研究进展;②在干热岩开采数值模拟技术方面,分别从岩心尺度多场耦合模型、储层尺度多场耦合模型和尺度升级方法3个角度,阐述了裂缝表征方法、数学模型及求解方法的研究进展;③在井筒热流体高效提取技术方面,讨论了井筒内流体闪蒸的原理、闪蒸流动特性研究的实验和数值模拟方法;④在干热岩地热发电技术方面,介绍了地热发电原理、发电系统类型和主要的应用市场。结论认为,EGS是一个技术密集型系统,但由于地下储层工况的复杂性和地面设备的不稳定性,机理研究往往与实际脱节,需与先导试验项目密切结合、互相指导,开展产—研结合模式,在不断往复中提高认知、突破关键点,从而大幅提升EGS的应用价值。

Enhanced geothermal system(EGS)is a primary method to develop geothermal resources stored in hot dry rock(HDR),but it faces several key problems restricting the large-scale commercial development of geothermal resources,such as unreasonable hydraulic fracture networks at high reservoir temperature,unclear multi-scale and multi-field coupling regularity,low heat extraction efficiency caused by the flashing flow in geothermal wells,and low thermoelectric conversion efficiency of geothermal fluid.Focusing on these major bottleneck problems,this paper systematically reviews and analyzes the research progress and development trend of four key technologies involved in the development of HDR geothermal resource by EGS.And the following research results are obtained.First,the research progress in the hydraulic fracturing technology for HDR reservoirs is illustrated in detail from the aspects of reservoir reconstruction methods,hydraulic fracturing network forming mechanisms and fracture propagation prediction models.Second,in terms of the numerical simulation technology of HDR development,the research progress in fracture characterization methods,mathematical models and solution methods is described from three perspectives including pore-scale multi-field coupled models,reservoir-scale multi-field coupled models and upscaling methods.Third,in terms of the efficient wellbore thermal fluid extraction technology,the principle of fluid flashing in geothermal wells and the experimental and numerical simulation methods for studying fluid flashing flow characteristics are discussed.Fourth,in terms of HDR geothermal power generation technologies,the principles of geothermal power generation,the types of power generation systems and the main application markets are introduced.In conclusion,EGS is a technology intensive system,but in view of complex working conditions in underground reservoirs,unstable ground equipment and isolation between mechanical research and practice,it is necessary to develop a production-research combined mode by combining and guiding mutually with pilot projects and get further cognition and break through key points based on continuous researches,so as to greatly improve the application value of EGS.