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Numerical simulation of reactive transport was validated in a core flooding experiment simulating conditions in a managed geothermal reservoir. Permeability was measured along a sandstone core prepared with anhydrite and subjected to a temperature gradient. Anhydrite was dissolved and precipitated in the cold upstream and hot downstream regions of the core, respectively. The numerical code SHEMAT was used to simulate coupled transport and chemical reactions at the temperature front (http://www.rwth-aachen.de/geop/shemat/). It comprises an extended version of the geochemical speciation code PHRQPITZ for calculating chemical reactions in brines of low‐high ionic strength and temperatures of 0–150°C. Permeability is updated to porosity via a novel, calibrated power‐law based on a fractal pore‐space model resulting in a large exponent of 11.3. Simulation results agree well with measured permeability. This both validates the model and demonstrates that the fractal relationship is crucial for a successful simulation of this type of reactive transport.

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Erbium was implanted with 160 keV at doses between 5x10 14 and 5x10 15 at/cm 2 into (0001) and at the same energies as above were annealed at 600° for 30 min and at 900°, 1000° C for 120 s using a proximity cap. The higher dose caused an almost complete amorphisation of the surface layer. After annealing indications of epitaxial regrowth were observed, however, the substitutional fraction remains substantially lower and the damage recovery is less complete.

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