Green chelating agent‒hydrofluoric acid synergy enables sustained mineral dissolution for near-wellbore stimulation in geological CO2 storage formations

Chemical stimulation to enhance near-wellbore permeability can be important where injectivity improvement is needed in low-permeability deep saline aquifer rocks relevant to geological carbon dioxide storage. Hydrofluoric acid-based stimulation accelerates silicate dissolution, but silica-rich secondary phases may impair permeability if dissolved silicon accumulates excessively. Here we present a stimulation strategy that combines a biodegradable glutamic-acid-derived chelating agent with ammonium bifluoride and brine flushing to sustain mineral dissolution while controlling the fate of dissolved silicon. Laboratory batch and flow-through experiments on sandstone and sandy siltstone from deep saline aquifers show that dissolved silicon can be temporarily removed from the aqueous phase as sodium hexafluorosilicate and then flushed out under diluted conditions. This process sustained mineral dissolution and increased both brine and nitrogen permeabilities by more than one order of magnitude within several hours, demonstrating promise for near-wellbore treatment of low-permeability storage formations. A strategy for sustained mineral dissolution may help improve near-wellbore injectivity in reservoir rocks relevant to geological carbon dioxide storage, according to a green chelating agent and hydrofluoric acid in batch and core-flooding experiments on deep saline aquifer sandstone and sandy siltstone.