Description
In deep geothermal reservoirs, fluid transport occurs primarily through fractures, especially in crystalline rocks with a nearly impermeable matrix. Particularly near boreholes, moderate to high flow velocities are observed in these fractures. Yet common hydraulic models often simplify the fluid dynamics, neglecting also the roughness of the fractures. To investigate the influence of flow rates and fracture roughness on the hydraulics, experiments were conducted in the F$^4$aT-Laboratory (Forced-Fracture-Fluid-Flow and Transport Laboratory). The roughness of various rock surface samples was analyzed. Key parameters, such as the Hurst exponent and height standard deviation, are measured. Several rock surface samples were compared and the results showed notable variations in roughness based on sample type. These values served than in boundary conditions for the hydraulic experiments. There, the hydraulics are tested in a flow-through setup at various flow rates (0.1 < Re < 100) with 3D-printed, upscaled roughness replica. We show the results of the roughness analysis from the measured rock samples, the upscaling process for the replica, the hydraulic results and their deviation from the simplified Cubic law at higher flow rates.
