垂直井闭循环地热系统热提取性能和注入优化数值模拟

Simulation of heat extraction and injection optimization from a vertical-well closed-loop geothermal system

为了评价单井闭循环的热提取性能,优化注入参数,文章针对中国东北典型场地,基于井筒-储层耦合数值模拟和场地的运行监测数据,分析了地热系统短期(热响应测试)和长期(一个供暖季)的提热性能,并优化了系统运行注入温度和流量。结果显示,典型东北地区1500 m长度的地热井在平均注入温度7℃,注入流量7.7 m^(3)/h条件下,换热孔出口平均功率为65.2 kW,一个供暖期出口与入口平均温差为4.9℃,地层温度降低影响最大范围约7 m,地层中的降温程度最大为23℃,并可以在非供暖期得到较好的恢复。在不考虑运行成本和可持续开发的情况下,注入温度越低、流量越大,获得的换热功率也越大。在调整注入温度为5℃和流量为6.3m^(3)/h的情况下,可获得同样的换热功率,此时的运行成本最低,比现有方案成本降低20%。考虑运行成本和可持续开发的优化设计对单井闭循环地热供暖具有现实意义。

To evaluate the heat extraction performance and optimize the injection parameters of a single-well Closed-Loop Geothermal System(CLGS),this paper analyzes the short-term(thermal response testing)and long-term(one heating season)heating performance of CLGS and optimizes operation parameters including injection temperature and rate,based on wellbore-reservoir coupling simulation and site operation monitoring data for a typical site in Northeast China.The results indicate that the mean heat extraction rate is 65.2 kW and the average temperature difference between the output and inlet is 4.9℃with an average injection temperature of 7℃and an injection flow rate of 7.7 m^(3)/h for a vertical well of 1700 m.At the end of a heating season,the maximum range for temperature reduction in the formation is approximately 7 m with the maximum temperature decrease up to 23℃,and it can recovery better during the non-heating period.Without considering operating costs and sustainable development,the low injection temperature and large injection rate result in high heat extraction rate.Setting the injection temperature to 5℃and flow rate to 6.3 m^(3)/h can minimize operating costs while meeting heating needs,reducing costs by 20%compared to the existing solution.The optimization design that considers operating costs and sustainable development has practical significance for a single well closed-loop geothermal system.