Thermo-acoustical-mechanical rock properties under in-situ conditions

• Applicant: Professor Dr.-Ing. Frank Wuttke
• Subject Area: Geophysics
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448842566

The aim of the project is to quantify the coupled thermo-acoustic mechanical behavior of rocks and their microstructural effects between minerals, grains and micro-cracks due to mechanical and thermal loading conditions under simulated in-situ pressure conditions with conducting a series of new experiments in the laboratory as well as the extension of the in-house numerical simulation model by anisotropic material behaviour. The goal is a deep understanding of the change of thermo-mechanical and acoustic rock parameters due to the change in the rock structure due to thermal and mechanical stress. High temperature and mechanical loads influence the microstructure of minerals, grains and induce micro-cracks, which significantly influence the thermo-acoustical-mechanical behavior of rock material. This behavior is even more pronounced and difficult to determine in often existing anisotropic and heterogeneous geomaterials.The investigation of this influence is currently possible only indirectly by ultrasonic waves, which are often calibrated to extracted, ambient pressure-free rock material. This type of thermo-acoustic correlations of rock parameters has been used extensively in geothermic, oil and gas storage and nuclear waste management studies, but this identification is poorly understood empirically and from a microstructural point of view. In addition to the described methods, there is a lack of measuring possibilities for the direct identification of thermal conductivities under in-situ conditions.In order to achieve the specified goals, a new development of the existing experimental triaxial thermo-acoustic-mechanical apparatus by an extension for stationary and transient thermal conductivity and heat capacity measurements under in-situ loads is planned. So far, this type of measurement is not possible within the scientific community. By considering in-situ pressure conditions, the existing rock fabric during the experiment and thus, the coupled thermal-acoustic-mechanical parameters will be different from previous stress-free analyses. In order to translate the experimental results into a theoretical and numerical simulation statement, further extended thermodynamic extended numerical simulations and micro- and meso-scale constitutive modeling of heterogeneous and anisotropic rocks are planned to determine the effective parameter. The novelty of the proposed work concerns: (a) the development of new constitutive models of thermal-acoustical-mechanical behavior of rocks; (b) the validation of the proposed model with new measurements of the thermal conductivity considering in-situ pressure and temperature; (c) the influence of the mineral grain size, particle size distribution, mineral composition, microcracking on the thermal-acoustical-mechanical properties under load and heating and (d) the effects of the microstructure of minerals on thermal-acoustical-mechanical properties.

• DFG Programme: Research Grants