Low-carbon and high-efficiency nanosheet-enhanced CO2 huff-n-puff (HnP) for heavy oil recovery

CO2 huff-n-puff (CO2-HnP) process is a promising technique for enhanced heavy oil recovery. The huff stage of this process involves the formation of foamy oil flow, characterized by dispersed CO2 bubbles within heavy oil, which plays a pivotal role in both oil recovery and CO2 sequestration. Maintaining the stability of foamy oil is crucial for the efficient implementation of CO2-HnP processes. Herein, ultrathin plate-shaped nanosheets are employed as stabilizers for foamy oil. Carboxyl-alkyl composite Janus nanosheets (SANs) are synthesized using a bottom-up approach. Comprehensive characterizations illustrate that SANs, owing to their amphiphilic and Janus nature, efficiently adsorb at the CO2-oil interface, thereby modifying interfacial properties and enhancing foamy oil stability even at low concentration (0.005 wt%). The incorporation of SANs extends the duration of foamy oil effect, resulting in a substantial enhancement of oil recovery efficiency from 30.7% to 39.4%, and an increase in CO2 storage factor from 6.5% to 7.8%, compared to conventional CO2-HnP processes. Micromodel experiments and molecular dynamics simulations show that SANs strengthen foamy oil stability by increasing interfacial activity and reducing CO2 diffusion rate. Overall, the multifunctional capabilities of SANs in interfacial modification offer promising prospects for enhanced oil recovery and optimizing CCUS efficiency.