Effects of fracture density, roughness, and percolation of fracture network on heat-flow coupling in hot rock masses with embedded three-dimensional fracture network. (September 2020)

• Record Type: Journal Article
• Authors: Yao, Chi; Shao, Yulong; Yang, Jianhua; Huang, Fan; He, Chen; Jiang, Qinghui; Zhou, Chuangbing
• Is Part Of: Geothermics. Volume 87(2020)
• Publication Date: 2020-09
• Subjects: Three-dimensional discrete fracture network -- Heat-flow coupling -- Percolation -- Fracture density -- Fracture roughness; Hydrogeology -- Periodicals; Geothermal resources -- Periodicals; Énergie géothermique -- Périodiques; GEOTHERMAL ENGINEERING; GEOTHERMAL ENERGY; GEOTHERMAL EXPLORATION; Geothermal resources; Hydrogeology; Periodicals; Electronic journals; 621.44
• DOI: 10.1016/j.geothermics.2020.101846
• Languages: English
• ISSNs: 0375-6505

Abstract

Highlights: This paper presents a model to reveal the heat transfer mechanism and simulate the heat-flow coupling process in fractured rock masses. The effects of fracture density and diameter on percolation probability are studied based on Monte-Carlo tests with each group for 10, 000 times. The effects of fracture density, roughness, and percolation of fracture network on heat-flow coupling in hot rock masses with embedded three-dimensional fracture network are studied. Abstract: This paper presents a model to reveal the heat transfer mechanism and simulate the heat-flow coupling process in fractured rock masses. Specifically, effects of fracture density, roughness, and percolation on heat-flow coupling are investigated systematically. The fractured rock masses are composed of a discrete fracture network and a rock matrix. Regarding the mesh discretisation for finite element analysis, the rock matrix is discretised into three-dimensional (3D) solid elements, whereas the discrete fractures are modelled by zero-thickness elements. Fracture and matrix elements share the same nodes. Considering the effect of temperature on fluid density and dynamic viscosity, a heat-flow coupled model of fractured rock masses is established with an embedded 3D fracture network. The reliability of the model is verified by comparing it with the analytical solution of a two-dimensional single-fracture heat-flow coupling problem. The effects of fracture density and diameter on percolation probability are studied based on Monte-Carlo tests with each group for 10, 000 times. Finally, numerical samples of the 3D discrete fracture network with different geometric parameters are generated to characterise fractured rock masses, and heat-flow coupling numerical simulation is conducted simultaneously. Results show that the percolation of the fracture network is the decisive factor affecting heat-flow coupling. The average outlet flow rate of the percolation network under the same fracture density is much larger than that of the nonpercolation fracture network, which results in a more rapid decrease in the outlet temperature. Other factors such as fracture roughness are also investigated. It is discovered that the effect of fracture roughness on heat-flow coupling is almost negligible for the nonpercolation fracture network model.