In this paper, the hydraulic and heat-transfer properties of two sets of artificially fractured granite samples are investigated. First, the morphological information is determined using 3D modelling technology. The area ratio is used to describe the roughness of the fracture surface. Second, the hydraulic properties of fractured granite are tested by exposing samples to different confining pressures and temperatures. The results show that the hydraulic properties of the fractures are affected mainly by the area ratio, with a larger area ratio producing a larger fracture aperture and higher hydraulic conductivity. Both the hydraulic apertureand the hydraulic conductivity decrease with an increase in the confining pressure. Furthermore, the fracture aperture decreases with increasing rock temperature, but the hydraulic conductivity increases owing to a reduction of the viscosity of the fluid flowing through. Finally, the heat-transfer efficiency of the samples under coupled hydro-thermal-mechanical conditions is analysed and discussed.
Hydraulic and heat transfer properties of artificially fractured rocks are the key issues for efficient exploitation of geothermal energy in fractured reservoirs and it has been studied by many previous researchers. However, the fluid temperature evolution along the flow path and rock temperature changes was rarely considered. This study investigated flow and heat transfer characteristics of two sets of fractured granite samples each with a single fissure. The samples were collected from a geothermal reservoir of Gonghe basin in Qinghai province in China. The results show that the larger area ratio, the higher hydraulic conductivity exhibited. Hydraulic conductivity of fractured rock masses is positively proportional to injection pressure, but inversely proportional with both confining pressure and temperature. In order to analyze heat transfer during the flow process, temperature distribution along the flow path in a fracture was monitored. The temperature of the fluid was determined to increase with distance from the flowing inlet. Increasing the temperature of the rock or decreasing the injection pressure will raise the temperature at the same location. Furthermore, in order to understand the heat transfer in rock mass, temperature distribution was observed by using an infrared thermal camera. Finally, the energy exchange efficiency during the flowing process was examined. The energy exchange rate increases continuously with the rock temperature, with an effective stress ratio of 1:2.
Bentonite, when used as buffer/backfill material in the deep disposal of high-level radioactive waste (HLW), could undergo desiccation shrinkage or even cracking due to the heat released from HLW, impairing the efficiency of the barrier system. Furthermore, in-service buffer materials are inevitably in contact with the groundwater, which sometimes contain high salt concentrations. The groundwater salinity may modify the properties of bentonite and hence affect the process of desiccation and its performance. To investigate this effect, in this study, a series of temperature-controlled desiccation tests was conducted on compacted specimens of Gaomiaozi (GMZ) bentonite preliminarily saturated with two different saline solutions (NaCl and CaCl2) at the concentration varying from 0.5 to 2.0 mol/L. The experimental results indicated that, as the concentration of saline solution increases, the initial saturated water content of bentonite decreases, whereas the residual water content at the completion of the desiccation test increases. The water evaporation rate is reduced for the specimens saturated with a high-concentration saline solution, and CaCl2 has a more significant influence on water evaporation than NaCl. The evolution of cracks on the sample surface during the desiccation process can be divided into four stages: crack growth, maintenance, closure, and stabilization; an increase in the salt concentration effectively inhibits crack development. It was shown that the infiltration of saline solutions alters the microstructure of bentonite by changing the arrangement of clay particles from a dispersed pattern to more aggregate state, which results in a decrease in shrinkage strain and shrinkage anisotropy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.