Investigation of Flow and Heat Transfer Characteristics in Fractured Granite

Abstract

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.