A Novel Multi‐Block High‐Cationic Density Side‐Chain Quaternary Ammonium Polymer: Preparation and Performance Evaluation of Clay Stabilizer for Efficient Water Injection

ABSTRACT To address the technical challenges of poor temperature resistance and the tendency to cause reservoir pore throat blockage in traditional organic cationic polymer (OCP) clay stabilizers, this paper successfully prepared a high cationic density branched ternary network polymer (PATSA) through emulsion polymerization, using (3‐acrylamidopropyl) trimethylammonium chloride (APTAC), styrene (St), and acrylonitrile (AN) as functional monomers, and 1,4‐divinylbenzene (DVB) as a crosslinking agent. The successful synthesis of PATSA was confirmed by infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy ( 1 H NMR); gel permeation chromatography (GPC) and polyelectrolyte titration tests showed a number average molecular weight ( M n ) of 5.83 × 10 4 and a heavy average molecular weight ( M w ) of 8.72 × 10 4 (PDI = 1.50), and cationic charge densities up to 4.6 meq/g. Zeta potential as well as contact angle tests show that PATSA achieves charge reversal and promotes aggregation of clay particles to inhibit hydration swelling through electrostatic adsorption of quaternary ammonium groups to the clay surface, while not causing reservoir damage due to wetting reversal. Zeta potential and contact angle tests demonstrate that PATSA achieves charge reversal through electrostatic adsorption between quaternary ammonium groups and clay surfaces, promoting clay particle aggregation to inhibit hydration swelling, while avoiding wettability alteration that could cause formation damage. The results of core flow experiments show that under the harsh conditions of high temperature (120°C), high clay content (9%), and high flow rate (0.5 mL/min), PATSA exhibits excellent clay stabilization performance, scouring resistance, and reservoir protection ability, and is able to effectively inhibit clay particle transport and reduce water‐sensitive reservoir damage, with a significantly better performance than the comparison reagents. The correlation pattern between water‐sensitive injury and clay particle size was revealed by clay particle size analysis; XRD analysis showed that the montmorillonite layer spacing shrank to a relative minimum after PATSA treatment (d 001 = 1.559 nm); SEM observations confirm that PATSA effectively inhibits clay swelling and dispersion through electrostatic adsorption and hydrophobic interactions, while producing fewer aggregated flocculated clay particles compared to conventional OCP treatment, thereby avoiding secondary plugging issues. The mechanism study shows that PATSA achieves effective prevention and control of clay hydration expansion and migration and mitigation of water‐sensitive reservoir damage through the synergistic mechanism of quaternary ammonium cation electrostatic adsorption, styrene hydrophobic barrier, and acrylonitrile cyano group. This study provides an innovative solution with both high efficiency and low risk for reservoir protection in water injection development of low permeability reservoirs.