Effects of fracture parameters and roughness on heat‐flow coupling in rock masses with two‐dimensional fracture networks

• Published in: Energy science & engineering 2021-08, Vol.9 (8), p.1216-1231
• Main Authors: Huang, Fan, Yao, Chi, Zhang, Xiaobo, Wu, Ligong, Shao, Yulong, Zhou, Chuangbing
• Format: Article
• Language: English
• Subjects: Apertures; Computational fluid dynamics; Confining; correlation function; Coupling; discrete fracture network; Exact solutions; Exponential functions; Flow rates; Flow velocity; Fluid flow; Fractals; Geometry; Heat conductivity; Heat flow; Heat transfer; Heat transmission; heat‐flow coupling; Hydraulics; joint roughness coefficient; Mathematical models; Outlet flow; Parameters; Reliability analysis; Rock masses; Rocks; Roughness; Roughness coefficient; Seepage; Simulation
• ISSN: 2050-0505; 2050-0505
• DOI: 10.1002/ese3.885

Discrete fracture network (DFN) is an effective means of describing the coupling of heat flow in an underground fractured rock mass. In this paper, an improved DFN is proposed by introducing the correlation function of fracture trace length and aperture, which is more consistent with the real fracture data. Next, based on the improved model, the influence of fracture roughness on the fluid flow and heat transmission was evaluated, and the relationship between the fracture aperture and the joint roughness coefficient (JRC) is established. Finally, based on the exponential function between confining pressure and aperture, the influence of confining pressure on the heat‐flow coupling process is considered in the improved model. Besides, the reliability of the model was verified by comparing with the analytical solution of the two‐dimensional single‐fracture heat‐flow coupling problem. The results show that under the same conditions, considering the correlation between the geometric parameters of the fracture, the seepage and heat transfer rates of the model increased, the outlet boundary flow reached the maximum value, and the average outlet temperature dropped rapidly. However, the fracture roughness reduces the outlet flow rate and the decline rate of average temperature. The confining pressure will lead to a decrease of about 3.5% in the outlet flow of the model, which is consistent with the seepage law in practical engineering. The model presented in this paper is an effective supplement to the two‐dimensional fracture network heat‐flow coupling model and can provide a theoretical basis and a numerical calculation tool for related underground rock mass engineering. Based on the conventional discrete fracture network, an improved discrete fracture network is proposed by introducing the correlation function of fracture trace length and aperture. Next, the relationship between the fracture aperture and the joint roughness coefficient (JRC) is established, and a heat‐flow coupling model considering the surface roughness of the fracture is proposed. Finally, an exponential function is used to characterize the change in the fracture aperture with confining pressure, and the influence on the fracture aperture with time is analyzed in the heat‐flow coupling process.