Christian-Albrechts-Universität zu Kiel, Deutschland
In this study, the effects of pressure and temperature on thermal conductivity of natural mono-minerals rocks in in-situ condition is investigated. Heat transfer in rock masses is one of the most crucial processes that needs to be considered in subsurface engineering applications, such as radioactive waste repositories, geothermal energy, and oil and gas storages. Despite the need, there is no direct method for measuring the change of thermal conductivity under high pressure and temperature loadings under in-situ conditions until now. For that target, existing steady-state tests are implemented into cube pressure experiments. Using a reference material for direct measurement of thermal conductivity, the thermal conductivity of 5 mono-mineral rock samples (Anhydrit, Mormor, Quarzit, Gips, Obsidan/perlit) under in-situ conditions are determined. The measurements are made over a temperature and hydrostatic pressure range of room temperature to 400 °C and 12 MPa to 400 MPa, respectively. The results indicate that the thermal conductivity of all samples increase with increasing pressure. The non-linear increase of thermal conductivity is found for rock samples at low hydrostatic pressure below 100 MPa. Additionally, the effect of micro-structure and mineralogical composition on thermal conductivity of mono-minerals rocks is discussed. The test results constitute the first systematic measurement of thermal conductivity under in-situ condition of different type of rocks and can be further used for the development of thermal models for predicting the thermal responses. To explain the measured effects the testing was simulated by fully coupled T-H-M Fracture-Network Lattice Element Method for homogeneous and heterogeneous materials. The simulations are also used for validation of the performed direct thermal conductivity measurement under overburden pressure.
long version here
