Preparation of CO2-Responsive Biobased Ternary Composite Microgel and Its Application in Reservoir Gas Channeling Plugging

In this paper, a biobased ternary composite microgel (CS-DP-AA) was designed and prepared, which was based on chitosan and had a reversible response to CO2. The synthesis of CS-DP-AA microgel was proved by infrared spectroscopy, chromatography–mass spectrometry, X-ray photoelectron spectroscopy, and Raman spectroscopy. The structure and properties of CS-DP-AA microgel before and after CO2 response were characterized by scanning electron microscope, transmission electron microscope, ultraviolet visible spectrophotometer, laser particle size analyzer, zeta potentiometer, and other instruments, and the CO2 response mechanism was explored. The results show that CS-DP-AA microgel had great CO2 response performance and stability, and the UV transmittance could still reach 90.01% (relative) at 268.98 h after CO2 response. Subsequently, the rheological properties of CS-DP-AA microgel were evaluated by a rotary rheometer, which shows that CS-DP-AA microgel after the CO2 response had obvious viscoelasticity. Although shear thinning appeared with the increase in shear rate, the CS-DP-AA microgel after the CO2 response still had good viscosity under high temperature, high pressure, and high shear rate, which proves that it had great rheological properties. On the other hand, the ability of CS-DP-AA microgel to plug gas channeling in reservoirs was evaluated by a dual-core parallel-core physical simulation experimental device. The results show that the CS-DP-AA microgel injected into the core can indeed react with the CO2 adsorbed in the pores of the porous core and plug the larger pores. After the response, the resistance coefficient of the system increased significantly, reaching 80 times that of the previous value. It has been shown that CS-DP-AA microgel can indeed block gas channeling in oil reservoirs, expand the sweep efficiency and swept volume of the CO2 gas drive, contribute to the recovery rate of oil reservoirs, and ensure the smooth development of oil reservoirs, which has a good application prospect in plugging gas channeling in oil reservoirs.