Produced water integration in CO₂ storage using different injection strategies: The effect of salinity on rock petrophysical, mineralogy, wettability and geomechanical properties

Optimizing CO₂ storage efficiency in Deep saline aquifers (DSA) involves improving each storage trapping mechanism, such as structural/stratigraphy, capillary/residual, mineral, and dissolution trapping mechanisms, while maintaining the reservoir integrity for long-term carbon capture and storage (CCS). These enhancements are driven by a series of geochemical reactions that favorably modify petrophysical, mineralogy, wettability, rock geomechanics of the rock, and dissolution of CO₂ in aquifer fluid. Three different CO₂ injection strategies have been identified and tested for optimizing CO₂ storage and efficiency- Continuous CO₂ injection (CCI), Water Alternating Gas (WAG), and Simultaneous scCO₂-brine Aquifer Injection (SAI). This study investigates the effect of integrating produced water (PW) into WAG and SAI strategies for CO₂ storage, emphasizing how the salinity of the injected water affects reservoir properties alterations in sandstone and limestone formations exposed to scCO₂. Experimental results show that high salinity levels accelerate mineralogy changes and wettability alteration, particularly in limestone, leading to porosity, permeability, and mechanical strength changes. While the SAI results showed more aggressive and detrimental changes in rock properties, WAG leads to slower reaction rates, a more stable and effective strategy with more gradual alterations in rock properties due to its ability to balance fluid flow and mechanical strength, hence offering greater stability for long-term CO₂ storage. Based on these findings, a 20–50 g/L salinity range is recommended to maintain reservoir integrity and reduce the negative impacts of salinity on CO₂ storage efficiency and storage. This study provides valuable insights for optimizing CO₂ storage in DSAs, enhancing environmental sustainability, and enhancing mineral trapping through more targeted geochemical reactions and lower changes in rock mechanical strength.