Nanosheet-Reinforced CO2 Foam Systems for CO2 Conformance Control: Effects of Reservoir Permeability and Heterogeneity

During CO2 flooding, foam systems show significant effects in controlling CO2 channeling. However, conventional CO2 in water foam systems has limited channeling control due to poor foaming ability and weak stability. A black nanosheet (BN)-reinforced CO2 foam (BN-CO2 foam) by blending BN with an aqueous foaming system was developed and evaluated. Static foaming performance evaluation, interfacial tension tests, and core flooding experiments by the method of in situ foam generation were conducted to systematically study the foaming ability, interfacial properties, emulsification performance, and permeability adaptability of this BN-CO2 foam system. Results showed that the addition of nanosheets (BNs) significantly enhanced the foaming performance of the CO2 foam, particularly in terms of foam stability (half-life period). When the BN concentration reached 0.005%, the BN-CO2 foam achieved a foam comprehensive index (FCI) of 58,500 mL·min, with a concurrent reduction of oil–water interfacial tension to 0.198 mN/m. Additionally, it exhibited excellent instant emulsification and rapid demulsification properties. The BN-CO2 foam system also demonstrated channeling control of CO2 in homogeneous core samples with permeabilities ranging from 10 × 10–3 μm2 to 1,000 × 10–3 μm2. Lower permeability cores showed earlier effective gas production control and better plugging effects. In heterogeneous reservoirs, BN-CO2 foam demonstrated significant fluid diversion capability at a permeability contrast of 2, mitigating reservoir heterogeneity. However, as the permeability contrast increased to 5, 10, and 20, the system’s adaptability declined, manifesting as ineffective sweep in low-permeability layers. This limitation is attributed to the subsurface foaming mechanism employed in this study. The work explicitly defines the operational window (permeability range and contrast thresholds) for in situ CO2 in water foam systems. For reservoirs with permeability contrasts exceeding 2, targeted conformance control agents (e.g., gel-assisted foams or nanoparticle stabilizers) are recommended to mitigate channeling. These findings bridge lab-scale insights to field applications, demonstrating the BN-CO2 foam system’s efficacy in CO2 mobility control.