Integrated geochemical modeling and experimental study of acid treatments for enhancing CO₂ injectivity: Implications for geological CO₂ storage

The precipitation of salts during supercritical CO₂ (scCO₂) injection remains a major challenge in geological CO₂ storage, leading to severe permeability impairment and injectivity loss. This study introduces a novel experimental and modeling framework to evaluate the efficacy of acid treatments in mitigating salt-induced permeability damage under representative reservoir conditions (1600 psi, 60 °C). Static batch experiments were conducted to evaluate the dissolution kinetics of salt precipitates in the presence of various acid solutions, enabling detailed analysis of pore-scale changes in geometry and mineral composition before and after treatment. Complementary core flooding experiments simulated dynamic flow conditions during CO₂ injection and acid treatment, providing insights into the transport and deposition of salt precipitates under hydrodynamic forces. Geochemical modeling using PHREEQC was applied to simulate CO₂-brine-rock-acid interactions, with equilibrium and reactive transport models predicting geochemical reactions and secondary precipitation during both CO₂ injection and acid treatment phases. The results reveal that salt precipitates can migrate under hydrodynamic forces, leading to deposition and re-suspension, which significantly impair CO₂ injectivity once immobilized. A key finding in this study was that precipitated salts were found to coexist with rock minerals during CO₂-brine-rock interactions, particularly during mineral dissolution phase. In terms of damage, scCO₂ injection caused substantial permeability damage, ranging from 7.84% to 71.86%, with more severe impairment observed at higher brine salinities. Porosity loss ranged from 11.42% to 33.66%, reflecting the extent of salt precipitation and mineral dissolution. Post treatment, the injectivity generally improved up about 45.99%, with acetic acid showing the best performance post treatment. Organic acids demonstrated a strategic advantage in acid treatments due to their slower reaction kinetics, enabling selective dissolution of salt precipitates while minimizing structural damage to the rock matrix. Furthermore, the susceptibility of minerals to acid attack was influenced by their iron content, and the formation of secondary precipitates was observed to vary with salinity and acid type. This study provides critical insights into optimizing acid treatment strategies to enhance CO₂ injectivity and storage efficiency in saline aquifers.