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An important objective for mature oilfields is the reduction in water production of oil wells, which is often accomplished by polymer flooding, a chemical method that involves the injection of polymers into fractures or high-permeability zones. Cationic and anionic polymers are studied by Caili Dai et al. as a moderate water shutoff agent for oil well treatment. The cover shows a cationic polymer initially adsorbed on mica, and an anionic polymer adsorbed on sites of the cationic polymer due to electrostatic interactions. The alternative adsorption of cationic and anionic polymers leads to the formation of a dense and stable adsorption multilayer on the mica surface. The adsorption multilayer can plug the high permeability zones. As a result, the residual oil is driven out, and oil recovery is improved. DOI: 10.1002/app.39462