Maximizing permeability of fractured volcanic rocks through chelating-agent-assisted and pH-controlled selective mineral dissolution

Abstract

Chemical stimulation of geothermal reservoirs through mineral dissolution using environmentally friendly chelating agents has been suggested as a new method to complement hydraulic stimulation. However, the permeability enhancement mechanism and optimal pH remain unexplored. In this study, we conducted flooding experiments on a fractured andesitic rock at 200 °C using 20 wt% N,N-bis(carboxymethyl)-L-glutamic acid (GLDA) solution, at pH 2–10. GLDA selectively dissolved Fe-bearing minerals (e.g., pyroxenes and magnetite) under acidic conditions and quartz in the groundmass under alkaline conditions, resulting in 9.1-fold and 98-fold permeability enhancements at pH 4 and 10, respectively. Therefore, the injection of a chelating agent with different pH values based on an investigation of rock mineralogy enhanced the permeability of volcanic rocks. These findings support the feasibility and effectiveness of chemical stimulation as a viable approach for widespread global utilization for enhancing geothermal systems.