深层垂直井同轴换热能力数值模拟分析

针对中深部（1 500~4 000 m）地热资源深井同轴“保水取热”科学评价问题，以COMSOL Multiphysics多物理场耦合数值计算软件为模拟平台，构建垂直单井岩-水耦合传热模型，以西安地区地层与地温特征为模拟背景，计算分析2种地温梯度（0.027、0.030℃/m）与4种注水口流速（0.25、0.50、0.75、1.00 m/s）工况下深层（3 500 m）地热单井套管换热能力。同时，建立5种井间距下的群井数值模型，分析不同井间距下群井中心井的出口温度变化规律。模拟结果显示:地温梯度越大，进出口温差越大，单位时间换热量与单位延米换热量越大；入口注水流速越大，进出口温差越小，但单位时间换热量与单位延米换热量越大，即地温梯度、流速越大，深层垂直钻孔套管换热的效率越高；西安地区3 500 m井深工况下，相邻地热井的间距为30 m时能够保证其地层温度不会相互干扰。研究结论可为深层地热开发利用提供科学参考。移动阅读 

Numerical simulation of coaxial heat transfer capacity of deep vertical wells

Aiming at the scientific evaluation of coaxial casing heat transfer of geothermal resources with medium burial depth(1 500-4 000 m), a rock-water coupled heat transfer model of a vertical single well was built based on the simulation platform of COMSOL Multiphysics software. Taking the stratigraphic and geothermal characteristics of Xi'an area as the simulation background, the heat transfer capacity of single well(3 500 m)casing under two different geothermal gradients(0.027℃/m and 0.030℃/m) and four flow velocities(0.25, 0.50, 0.75, 1.00 m/s) was calculated and analyzed. Meanwhile, the numerical models of group wells with five kinds of well spacing were established, and the variation law of outlet temperature of the central group wells with different well spacing was analyzed. The simulation results show that the greater the geothermal gradient, the bigger the temperature difference between the inlet and the outlet, and the larger the heat transfer per unit time and the heat transfer per unit length of borehole. The larger the inlet injection velocity, the smaller the temperature difference between the inlet and the outlet, and the larger the heat transfer per unit time and per unit length of the borehole, which indicating that the higher the geothermal gradient and the flow velocity, the higher the heat transfer efficiency is. Under the deep working condition of 3 500 m in Xi'an area, when the distance between adjacent geothermal wells is 30 m, it would ensure that the formation temperature will not interfere with each other. The conclusion in this paper would provide scientific reference for the development and utilization of the deep geothermal resources.