A waste-integrated hydroxyethyl cellulose–brine electrocoagulation platform for CO₂ uptake and enhanced crude oil recovery

Managing high-salinity reject brine, CO₂ emissions, and declining oil recovery presents interconnected challenges across the water–energy nexus. This study investigates an integrated waste-derived hydroxyethyl cellulose–electrocoagulation–CO₂ (HEC─EC─CO₂) platform for brine treatment, gas-phase CO₂ uptake, solid recovery, and enhanced oil recovery (EOR). Electrocoagulation under continuous CO₂ injection modified the brine system and generated carbonate- and hydroxide-containing recovered solids, supported by SEM–EDS, XRD, and Raman characterisation. Average gas-phase CO₂ removal reached 77.1%, corresponding to a gross uptake of 16.49 g CO₂/L of treated brine. The treated formulations exhibited modest, non-monotonic rheological modification. At 110 °C, oil–water IFT decreased from 13.566 mN/m for seawater to 0.054 mN/m for the 2000 ppm formulation, while the aqueous-phase contact angle decreased from approximately 96–98° to 9.4°. Experimental core flooding at 80 °C increased oil recovery from 62.23% OOIP after seawater flooding to 78.24% OOIP after tertiary injection, corresponding to 16.02 percentage points of incremental recovery. Complementary CMG STARS simulations predicted 70–75% OOIP, consistent in magnitude with the experimental recovery but not formally history-matched. Overall, the results demonstrate the proof-of-concept potential of the integrated platform for brine modification, CO₂ uptake, and tertiary oil recovery.