中深层地热Ｕ型井地埋管换热器的试验研究

地热能作为一种非碳基能源,具有储量丰富、清洁可再生等特点,开发利用地热能有助于碳达峰的实现。在中深层地源热泵领域,我国主要以单井同轴管为主,而相对高效的中深层地热U型井地埋管案例屈指可数。为了了解中深层地热U型井地埋管换热性能及井下换热参数变化,完成了新型的Ｕ型井地埋管换热器工程,并在此基础上进行了实验研究。首先,开展了地温测量,确定了研究区的地层温度,根据热储的物性条件选取了水平井段及对接位置；其次,分析空载循环试验工况下循环水的流量及井下温度的变化情况,研究了负载工况下供回水温度、流量、换热量、不同井段对换热的贡献率、井下温度的动态变化、U型井的恢复能力等因素。实验结果表明,中深层Ｕ型井地埋管换热器井底温度会随运行时间增长而降低,流量大且回水温度较低的情况下,换热器的换热量比较高,最高为1336.8kW；回水井对换热量的增加有限,每百米增加0.12℃,实际工程中可以考虑减小口径,降低建设费用。U型井地埋管换热器的地温恢复能力较强,停止运行24h左右井底温度与初始温度差为-13℃。研究结果有助于研究人员对中深层Ｕ型井地埋管换热器有更进一步的认识,从而推动中深层地热能的健康可持续发展。

Experimental investigation on U-type ground heat exchanger of medium-deep geothermal energy

As a non-carbon-based energy source, geothermal energy has the characteristics of abundant reserves, clean and renewable, and the development and utilization of geothermal energy will help achieve carbon peaking. In the field of medium and deep ground source heat pumps, China mainly focuses on single-well coaxial pipes, and there are only a few cases of relatively efficient medium and deep geothermal U-shaped underground pipes. In order to understand the heat transfer performance of underground pipes and the change of downhole heat exchange parameters of medium and deep geothermal U-shaped wells, the new U-shaped underground pipe heat exchanger project was completed, and experimental research was carried out on this basis. Firstly, the ground temperature measurement was carried out, the formation temperature of the study area was determined, and the horizontal well section and docking location were selected according to the physical conditions of heat storage. Secondly, the flow rate of circulating water and the change of downhole temperature under no-load cycle test conditions were analyzed, and the factors such as supply and return water temperature, flow, heat exchange, contribution rate of different well sections to heat exchange, dynamic change of downhole temperature, and recovery ability of U-shaped wells under load conditions were studied. The experimental results show that the temperature at the bottom of the buried pipe heat exchanger in the medium and deep U-shaped wells will decrease with the increase of operating time, and the heat exchange of the heat exchanger is relatively high when the flow rate is large and the return water temperature is low, up to 1336.8kW; the increase in heat exchange of the return well is limited, increasing by 0.12°C per 100 meters. The ground temperature recovery ability of the U-shaped underground pipe heat exchanger is strong, and the difference between the bottom temperature and the initial temperature is -13°C for about 24h after stopping operation. The results of the study will help researchers to have a better understanding of the buried tube heat exchanger in medium and deep U-shaped wells, so as to promote the healthy and sustainable development of medium and deep geothermal energy.