Numerical analysis on the coupling of transient fluid flow and heat transfer within the complex fracture network of coal based on 3D reconstruction of CT images

After being abandoned, coal mines still have the potential of geothermal energy development. This study is aimed at exploring the seepage and heat transfer of the complex fracture network in coal rock within abandoned coal mines. To achieve this aim, the complex fracture network and matrix in coal were modeled by 3D reconstruction of CT images, and a coupling model of transient fluid flow and heat transfer was established. The results show that the complexity of the fracture network considerably affects the ETC of coal as the fracture rate increases from 4.10 % to 21.64 %, and the ETC anisotropy of gas-containing coal is up to 1.7 times as high as that of liquid water-containing coal. In the liquid water model, the intrusion direction of liquid water exerts a notable influence on the distribution of dominant migration path (DMPs). The transient heat transfer process can be categorized into three stages, i.e., the primary action stage of DMPs, the attenuation stage of DMPs, and the stable heat transfer stage. In the gaseous model, the fracture network exerts a relatively minor influence on the overall dynamic temperature distribution, and the temperature fields are distributed in similar manners across varying fracture networks.