An investigation into the effects of anisotropy and heterogeneity of fracture permeability on flow and thermal transport.
Hoeven, J.A. van der
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To be able to predict the viability of geothermal reservoirs it is important to know how hydrodynamically stimulating a reservoir will alter the system and how fluids will flow through this reservoir. Making an accurate prediction is difficult due to the natural heretogeneity and complexity of the subsurface. In addition, flow through the deep subsurface is often dominated by fractured media rather than by aquifers. This added layer of complexity combined with the inherit difficulties of gathering data in the deep subsurface result in a research field where numerical simulations are crucial. This thesis focusses on the natural heterogeneity of the system and aims to connect the processes on the fracture scale to results on the reservoir scale. The investigation consists of three sequential parts. Firstly, 2D cases with a single fracture where the effects of fracture wall roughness and shear on the permeability of the fracture are investigated. Secondly, a 3D case with a simple grid to show the effects of fracture with an anisotropic permeability on flow and heat transport. Finally, a 3D simulation to indicate the effects of stress on flow and heat transport through a reservoir. Shear is found to increase the permeability of a fracture, with the largest increase in the direction perpendicular to the shear. Depending on the initial state of the fracture and the length of shear the permeablility perpendicular to the direction of shear is up to one order of magnitude larger compared to the permeability parallel to the direction of shear. This difference can determine whether flow occurs predominantly through the fracture or through the semi-permeable rock matrix.