CO ₂ -Responsive Expansion Polymer Gel for Channel Blocking in Low-Permeability Reservoirs

In recent years, driven by the dual demands of achieving carbon neutrality and enhancing the efficient development of low-permeability reservoirs, CO2 flooding has attracted increasing attention. However, due to strong reservoir heterogeneity, CO2 preferentially flows through high-permeability pathways, leading to severe gas channeling and a significant reduction in sweep efficiency. The objective of this work is to develop a CO2-responsive polymer gel that can expand upon exposure to CO2, thereby enhancing its ability to block gas channeling pathways. A CO2-responsive polymer was first synthesized and structurally characterized, followed by the preparation of a CO2-responsive polymer gel blocking system. Its rheological properties, CO2-responsive expansion behavior, channel blocking, and enhanced oil recovery performance were systematically investigated. Furthermore, the channel blocking and enhanced oil recovery mechanism of the CO2-responsive polymer gel were elucidated using nuclear magnetic resonance techniques. The results demonstrate that the prepared gel blocking system exhibits excellent CO2-responsive behavior, with significant increases in viscosity and viscoelastic moduli after response, both of which are higher than those of an industrial HPAM polymer gel. After immersion in acidic simulated formation water for 48 h, the gel mass increased to 2.94 times its initial value. In addition, the system shows a remarkable improvement in channel blocking and enhanced oil recovery performance. This work provides a new technical approach and theoretical basis for the application of polymer gels in CO2 flooding channel blocking.