Work

Permeability evolution during long-term matrix acidification of sandstone under reservoir conditions

Year: 2026

Type: article

Abstract: Matrix acidification is widely applied to enhance near-wellbore transmissivity in reservoir rocks; however, its efficiency remains difficult to predict because long-term fluid–rock interactions under realistic reservoir conditions are not fully understood. The combined effects of chemical reactions and time-dependent deformation during prolonged acid injection remain insufficiently constrained. This study investigates permeability evolution in sandstone during prolonged injection of dilute hydrochloric acid (0.0375 wt% HCl; pH 2.0) under controlled temperature and stress conditions representative of geothermal reservoirs.,Five flow-through experiments were conducted using a thermo-triaxial device, allowing coupled thermo–hydro–mechanical conditions to be maintained over extended durations. Permeability, axial and radial strain, and fluid chemistry were continuously monitored, while mineralogical changes and dissolved element concentrations were analyzed before, during, and after testing. After approximately 25 days of continuous flow, permeability increased in four of the five samples, although the magnitude and timing of the response varied between experiments. Permeability evolution cannot be explained by mineral dissolution alone but reflects the coupled influence of spatially localized fluid–rock reactions, thermally enhanced creep, and stress-controlled pore reorganization.,These results demonstrate that long-term permeability evolution during geothermal acidification is governed by interacting thermo–hydro–mechanical–chemical (THMC) processes rather than purely geochemical effects, providing new constraints for reservoir stimulation strategies and reactive transport modelling approaches.

Source: Geothermics

DOI: 10.1016/j.geothermics.2026.103699