The article is devoted to the issue of a low sweep efficiency in the heterogeneous terrigenous reservoirs containing remaining oil. Water plugging operations that redirect the injection fluid flows into unswept zones, are one approach to enhancing the oil recovery in these reservoirs. The commonly used chemical reagents in these treatments are acrylate polymer solutions. The polymer solutions must reach the target water-saturated zones and form a strong gel barrier there. Furthermore, the polymer compositions should have a low initial viscosity to provide a good injectivity and penetration ability. Therefore, the methods of adjusting the gelation time are necessary. There are numerous studies in modern scientific society devoted to the study of water-plugging polymer compositions. However, aspects, such as the effect of the hydrogen index on gelation, have received insufficient attention. In this paper, we describe the features of the developed polymer composition, based on a hydrolyzed polymer of acrylonitrile with a controlled gelation time for the chemically enhanced oil recovery. The component composition and the concentration levels were selected, based on the alterations in the hydrogen index of the polymer solution. It was scientifically proven that by adhering to a neutral hydrogen index, it is possible to improve the properties of the polymer composition. Moreover, using a model of a heterogeneous reservoir, it was confirmed that the proposed polymer composition achieves selective plugging. As a result of the polymer gel treatment, the water cut decreased by 4% and the displacement coefficient of oil increased by 20%, in comparison with the effect of the original composition without a gel-time modifier.