关中地区中深层同轴套管换热器换热能力及提升措施研究

Heat transfer capacity of middle-deep coaxial casing heat exchanger in Guanzhong area and the improvement measures

同轴套管换热器是实现中深层地热能井下高效取热技术之一,其换热能力对地热系统的可持续开发至关重要。以关中地区为例,考虑地层不均匀性建立中深层地热井同轴套管传热计算模型,研究注入温度、注入流量、埋管深度等因素对其取热性能的影响,探讨间歇开采工况下注入温度和注入流量对热储层温度恢复的影响。结果表明:随着注入流量增加,出口流体温度下降,但整个系统的取热功率提高;当注入温度较高时,可有效提高出口流体温度,但系统取热功率降幅较大;随着地层深度增加,出口流体温度和取热功率逐渐上升;减小内管管径,增加外管管径,可有效提高出口流体温度和取热功率;热储层温度恢复能力随注入流量和注入温度的升高而提高;通过降低内管导热系数或选用双内管结构可以降低内管流体沿程温度损失,提高系统的出口流体温度。

The coaxial casing heat exchanger is one of the technologies to realize high efficient heat extraction in the middle and deep geothermal energy wells, and its heat transfer capacity is crucial to the sustainable development of geothermal system. Taking Guanzhong area as an example, the heat transfer model of coaxial casing heat exchanger in middle-deep geothermal wells is established considering the formation inhomogeneity, and the effects of injection temperature, injection flow rate, buried depth and other factors on its heat extraction performance are studied. The influences of injection temperature and injection flow rate on thermal reservoir temperature recovery under intermittent production condition are discussed. The results show that, the outlet fluid temperature decreases with the increasing of injection flow rate, but the heat extraction power of the whole system increases. Increasing the injection temperature can improve the outlet fluid temperature, but the system heat extraction power decreases greatly. With the increasing of formation depth, the temperature of outlet fluid and heat extraction power increase gradually. Reducing the inner pipe diameter and enlarging the outer pipe diameter can effectively improve the temperature of outlet fluid and heat extraction power. The temperature recovery ability of the thermal reservoir increases with the injection flow and injection temperature. Reducing the thermal conductivity of inner pipe or choosing double-layer inner pipe structure can reduce the fluid temperature loss along the inner tube and increase the outlet fluid temperature.