SP Monitoring of an Acid Stimulation of the Soultz Geothermal Reservoir

SP monitoring of a sequence of water-acid-water injections over a span of three weeks in the Soultz geothermal reservoir shows a decrease of the surface electric potential during the acid stimulation. This requires a negative electrokinetic coupling coefficient, which is predicted by the theory for fluids with very low pH. Post-acid injections also yielded negative signals that are likely caused by electrochemical processes during the increase in ionic content of the injected water. These results have some importance when considering using acid stimulations for geothermal reservoirs in a production phase.