Exploration of Flyash‐Reinforced <scp>3D</scp> Hydrogels: Salt‐Tolerant Water Swelling for Optimized Water Diversion

ABSTRACT Hydrogels plug high‐permeability zones by swelling in profile control, redirecting water to low‐permeability areas. This study developed a novel 3D composite hydrogel using acrylamide, flyash, and sodium carboxymethyl cellulose for enhanced swelling under extreme conditions. Swelling behavior was optimized under varying salinity, pH, temperature, and particle size. Under optimal conditions (8% NaCl, pH 12.0, 120°C, particle size ≤ 0.125 mm), the hydrogel achieved a remarkable swelling ratio of 158.90 g g −1 , surpassing conventional PAM's 108.60 g g −1 . In contrast, the salt‐tolerant swelling capacity of the hydrogel was only 39.80 g g −1 under pH 6.0 conditions. Core flooding tests showed 93.3% plugging efficiency in sand packs, with excellent profile control and water shutoff. Notably, the hydrogel showed significantly enhanced salt‐resistant swelling at pH 12.0. This performance improvement primarily stems from the targeted hydrolysis reaction of flyash in strong alkaline environments. During this hydrolysis process, the generated anions effectively reduce Na + concentration and mitigate osmotic pressure, while the hydrolysis of CONH 2 groups produces COO − under alkaline conditions. This enhances the electrostatic repulsion between polymer chains, expanding the 3D network and thereby greatly increasing swelling. This study promotes a circular economy by repurposing industrial waste into smart hydrogels for practical oilfield water control applications.