Effect of reservoir seepage on heat transfer performance of a single-well downhole coaxial geothermal heat exchanger

doi:10.16085/j.issn.1000-6613.2024-0878

Abstract

Abstract:

Downhole coaxial heat exchangers extract heat but do not consume water, solving the problems such as low reinjection rate, thermal and chemical pollution faced by the traditional pumping and reinjecting geothermal brine development method. The downhole coaxial heat exchangers are promising for geothermal wells converted from abandoned oil or gas wells. Geothermal brine seepage affects the reservoir temperature field which in turn affects the heat extraction characteristics of the downhole coaxial heat exchangers. A numerical model of a coaxial heat exchanger coupling heat transfer and seepage was constructed in this work. The temperature distribution of the geothermal reservoir under various seepage parameters was investigated by taking an abandoned well in Daqing oil field as an example. The influence of the reinjection parameters on the heat transfer characteristics of the coaxial heat exchanger was also discussed. The heat transfer process of the downhole heat exchanger was synergistically affected by the heat conduction in rock and seepage heat mass transfer. When the speed of seepage reached 10^-6m/s, the outlet temperature of the coaxial heat exchanger was increased by 1.1℃ and the heat extraction power was increased by 4.3% compared with that in the case of no seepage. When the speed of the seepage reached 10^-5m/s, the outlet temperature was further increased by 9.7℃ and the heat extraction power was increased by 65.2%. The thermal influence radius of heat extraction from the wellbore was greatest at a seepage speed of 10^-5m/s and a porosity of 28%, which was about 4.5 times greater than in the absence of seepage. At lower reinjection temperatures and higher flow rates, the response of the heat extraction power was amplified, and the heat extraction power of the heat exchanger was increased, but the outlet temperature was reduced.

Key words: heat transfer, porous media, numerical simulation, geothermal energy, seepage, coaxial heat exchanger, heat extraction characteristics

摘要：

单地热井同轴换热器只取热不耗水，解决了抽灌采热方式面临的回灌困难、地表热污染和化学污染等问题，在废弃油气井改造地热井等领域具有广阔的应用前景。地下水渗流影响储层温度场，进而影响单井换热器的取热特性，本文构建了中深层单地热井同轴换热器的热渗耦合模型，以大庆油田一废弃油井改造的地热井为例，探讨了不同渗流参数下储层的温度分布，揭示了渗流作用下工质回注参数对同轴换热器取热特性的影响规律。井下换热过程受岩体导热和渗流热质传递的协同影响，当渗流速度低于10^-6m/s时，井下传热以岩体导热为主，换热器出口温度较无渗流时仅升高1.1℃，取热功率增加4.3%；渗流速度达10^-5m/s时，储层内热流密度提高，换热器出口温度可升高9.7℃，取热功率提高65.2%。井筒取热的热影响半径在渗流速度为10^-5m/s、孔隙度为28%时最大，约为无渗流时的4.5倍。在回注温度低、循环水流量大时，系统对回注参数变化的响应幅度大，换热器取热功率提高，但出口温度降低。

关键词: 传热, 多孔介质, 数值模拟, 地热能, 渗流, 同轴换热器, 取热特性

CLC Number:

TK52

YANG Xinliu, LIU Qiang, CAO Qian, CUI Yueming, FANG Chaohe. Effect of reservoir seepage on heat transfer performance of a single-well downhole coaxial geothermal heat exchanger[J]. Chemical Industry and Engineering Progress, 2025, 44(7): 3860-3868.

杨心柳, 刘强, 曹倩, 崔岳铭, 方朝合. 储层渗流对单地热井同轴换热器取热特性的影响[J]. 化工进展, 2025, 44(7): 3860-3868.

Figures/Tables 15

References 30

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参数	数值
井深/m	1800
外管管径/mm	123
外管壁厚/mm	10
内管管径/mm	75
内管壁厚/mm	7.5
外管壁热导率/W·m^-1·K^-1	4.5
0~200m新型保温材料内管热导率/W·m^-1·K^-1	0.05
200~800m无规共聚聚丙烯(PP-R)内管热导率/W·m^-1·K^-1	0.21
800~1760m PP-R内管热导率/W·m^-1·K^-1	0.24
1760~1800m 304不锈钢内管热导率/W·m^-1·K^-1	15
地热储层热导率/W·m^-1·K^-1	1.682
地热储层密度/kg·m^-3	2631.5
地热储层恒压热容/J·kg^-1·K^-1	886.89
基础工况下进水温度/℃	5
基础工况下循环流量/m³·h^-1	10

参数	数值
井深/m	1800
外管管径/mm	123
外管壁厚/mm	10
内管管径/mm	75
内管壁厚/mm	7.5
外管壁热导率/W·m^-1·K^-1	4.5
0~200m新型保温材料内管热导率/W·m^-1·K^-1	0.05
200~800m无规共聚聚丙烯(PP-R)内管热导率/W·m^-1·K^-1	0.21
800~1760m PP-R内管热导率/W·m^-1·K^-1	0.24
1760~1800m 304不锈钢内管热导率/W·m^-1·K^-1	15
地热储层热导率/W·m^-1·K^-1	1.682
地热储层密度/kg·m^-3	2631.5
地热储层恒压热容/J·kg^-1·K^-1	886.89
基础工况下进水温度/℃	5
基础工况下循环流量/m³·h^-1	10