Onsite experimental simulation of brine injection into a clastic reservoir as applied to geothermal exploitation in Germany

Results from two onsite core flood experiments are presented addressing permeability development of a clastic reservoir to brine flooding. Sandstone samples were percolated with anoxic thermal brines to simulate injection during geothermal exploitation. Petrographic studies of the cores before and after the experiment and chemical investigations of the thermal water have shown that despite good initial petrophysical properties, injection of geothermal brines led to a permeability decrease of the core plugs. The experiment with oxidized water showed a permeability decrease resulting in a total loss of permeability due to precipitation of Fe hydroxide. The decrease is dependent on particle size and concentration, pore throat size and flow rate. The decline of permeability during the second percolation experiment with original thermal water can be explained by deposition of small particles such as fragments of feldspars and quartz into the porous medium.