Preparation of Selective-Plugging Microgel Particles for CO2 Conformance Control in Supercritical Conditions

Summary Carbon dioxide (CO2) flooding is a promising technology for reducing carbon emissions and enhancing oil recovery in low-permeability reservoirs. However, the prominent viscosity difference between CO2 and crude oil leads to viscous fingering. Furthermore, superimposed with reservoir heterogeneity, the channeling of CO2 is further intensified, causing premature CO2 breakthrough. Then, severe gas channeling occurs, significantly limiting the sweep efficiency. The application of gel particles to control gas channeling faces significant challenges due to the strong extraction effect and acidic environment associated with CO2, which deteriorate the swelling capability and structural stability of conventional gel particles. Consequently, existing CO2-resistant gel particles often fail to control the channeling of CO2 effectively and sustainably in low-permeability reservoirs. In this study, gel particles with CO2 affinity and swelling capability in CO2 environments were developed to enhance the stability and enable selective plugging. A polymer incorporating polydimethylsiloxane (PDMS) segments was designed, and a CO2-affinitive gel particle system was constructed via emulsion polymerization. Analysis of particle-CO2 interactions showed that the CO2-affinitive gel particles exhibited an attractive interaction energy, the magnitude of which was 31.83% greater than that of polyacrylamide (PAM) gel particles. Microstructural and particle size analyses revealed that the particles possess comparatively uniform initial diameters with good dispersibility. Thermal stability testing indicated that the gel particles could withstand temperatures up to 363.5°C under CO2 atmosphere. Coreflooding tests showed that at 0.5 wt% concentration, the gel particles achieved a plugging rate exceeding 80% in the presence of CO2. Furthermore, once a nitrogen (N2) slug was injected after the CO2 slug, it led to a 44.50% reduction in plugging efficiency and partial restoration of the rock permeability, attributable to significant contraction of gel particles previously swollen by CO2. Overall, the CO2-affinitive gel particles offer an efficient solution for mitigating CO2 channeling, expanding the swept volume, and ultimately improving the recovery efficiency of low-permeability reservoirs under CO2 flooding.