基于热流固耦合的单井增强地热系统数值模拟

Numerical simulation of a single-well enhanced geothermal system based on thermal-hydraulic-mechanical coupling

为提高深井换热器的取热效率,借鉴干热岩的开发思路,本文提出了一种单井增强地热系统。对单井套管底部岩体进行小范围压裂改造,将单井套管由封闭式系统改为开式系统来提高单井系统的取热性能。建立了热-流-固耦合的三维非稳态数值模型,研究了单井增强地热系统的系统性能表现和各关键参数的影响。结果表明:与传统深井换热器相比,单井增强地热系统的取热性能有较大提升,相同注入工况下,生产温度和取热功率分别提高了62.21℃和2 612.99 kW;从地热工程周期和优化角度出发,单井增强地热系统流量控制在10 kg/s较为适宜,过小的单井增强地热系统流量导致取热效率较低,过大使得系统运行寿命较短;增大井筒封隔间距、减小内管导热系数是提高系统取热性能的有效方法。本文研究可为单井增强地热系统的理论分析和实际应用提供参考。

To improve the heat extraction efficiency of deep well heat exchangers,a single-well enhanced geothermal system(SEGS) was proposed using the development idea of hot dry rock for reference.The rock mass at the bottom of a single-well casing was reformed by small-scale fracturing;the single-well casing was changed from a closed system to an open system to improve the heat extraction performance of a single-well system.A thermal-hydraulic-mechanical coupling three-dimensional unsteady-state numerical model was established to study the system performance of SEGS and the influence of various key parameters.Results show that compared with the traditional deep well heat exchanger,SEGS has a greatly improved heat collection performance.Under the same injection condition,the production temperature and heat collection power are increased by 62.21 ℃ and 2 612.99 kW,respectively.In terms of a geothermal engineering cycle and optimization,it is more appropriate to control the SEGS flow at 10 kg/s.A small flow of SEGS decreases heat extraction efficiency,and a large flow shortens service life.Increasing the wellbore spacing and reducing the thermal conductivity of the inner pipe effectively improves the heat transfer performance of the system.Herein,we provide a reference for the theoretical analysis and practical application of SEGS.