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Abstract

For identification of the impact of salt-free and soured fluids injected for hydraulic stimulation on the about 4,000 m deep Rotliegend sandstones, cross-flow tests were carried out in combination with petrographic and fluid-chemical investigations. As a consequence of the swelling and the potential mobilisation of the clay minerals, a reduction of the permeability was expected. However, the test did not produce any significant change of the permeability for the cross-flow of differently conditioned waters under modified p/T conditions. But there could be proven the mobilisation of heavy metals and the solution of carbonate cement. As these cement minerals form a small fraction only in the total rock and due to their uneven distribution, no damage of the aquifer has to be expected. A local transport of finest particles could be observed which is probably connected with the carbonate solution. In case of suddenly increasing pore pressures, there is a risk of particle discharge, so that damaging of the pore reservoir cannot be excluded due to this small-scale transport of particles.