CO2 solubility and mineral trapping behavior in high-salinity reservoirs

Abstract

CO₂ solubility and mineral trapping behavior are critical to the stability and effectiveness of integrating CO₂ geological storage synergistically with gas field produced water (GPW) reinjection, a promising strategy for achieving co-benefits in pollution mitigation and carbon emission reduction. To investigate CO₂ solubility-mineral trapping during co-injection with GPW–characterized by high salinity and complex ion composition–a series of CO₂-GPW-rock interaction experiments and geochemical simulations were conducted using sandstone and limestone samples, together with simulated GPW of salinities ranging from 47.6 to 225.5 g/L. The results indicate that: (1) CO₂ solubility-mineral trapping behavior is governed primarily by CO₂ pressure, injection method, and GPW salinity, and is further influenced by calcium concentration and rock mineralogy. Under the experimental conditions, the CO₂ solubility-mineral trapping capacity ranged from 9.03 to 11.01 g/L, with corresponding trapping proportions between 74.56% and 87.38%; (2) within a closed CO₂-GPW-rock reactive system, the time-dependent CO₂ solubility-mineral trapping proportion can be described by the cumulative Weibull model. The CO₂ solubility-mineral trapping capacity increases with increasing CO₂ pressure but decreases with increasing GPW salinity. A slight elevation in calcium concentration enhances CO₂ solubility-mineral trapping at low CO₂ pressures, despite concurrent increases in ionic strength and brine salinity. When the GPW salinity remains constant, the variation in calcium concentration exerts only a limited influence on CO₂ solubility-mineral trapping; (3) a higher reactive mineral content in the reservoir enhances CO₂ solubility-mineral trapping, and intermittent injection significantly improves this process; (4) the cumulative solubility-mineral trapping capacity can reach 22.13–38.01 g/L, representing 2.28–3.04 times the capacity achieved under single-injection conditions. These findings underscore the importance of carefully selecting storage sites and designing injection schemes in CO₂ geological storage operations.