Leaching of Rock Fractures: Laboratory and Field Tests for Borehole Heat Stores

摘要

The aim of the project was to increase the hydraulic conductivity of fractured rock by pumping a leaching fluid (NaOH) through rock fractures. The field test was carried out in a borehole heat store, consisting of 19 vertical boreholes to a depth of 15 m in gneissic rock. The duration of the leachage test was 16 weeks. The idea of the project, that a NaOH-solution would leach and thereby widen the fractures, was not fulfilled. On the contrary, the fractures were sealed as the leaching test went on. The explanation to this is that the leaching rate was higher than expected, the leaching fluid was saturated and the dissolved minerals precipitated. The conclusion of the project is that a leaching of rock as described in the paper should be combined with a deposition tank for the clogging material in order to avoid precipitation in the rock fractures.