Abstract:

To meet the requirements of channeling plugging and enhanced oil recovery, the performance of oil-based foam channeling plugging systems formed by adding different surfactants （SDS, SDBS, Span20, and OP-10） in diesel was systematically evaluated, and their oil displacement mechanisms were discussed. The foam was prepared by high-speed stirring method. Combined with the constant temperature experiment under CO₂ protective atmosphere, the foam volume, half-life and foam composite index were analyzed. The research results showed that SDBS performed best at the mass fraction of 0.3%, at which its foam volume in diesel was 215 mL, half-life was 215.4 s, and foam composite index was significantly higher than that of other surfactants. SEM showed that there was lamellar liquid crystal structure in SDBS foam, and the film thickness of foam was 1.5-2.0 μm. Oil-based CO₂ foam could achieve profile control by selectively blocking the high-permeability channels through the Jamin effect. The profile control, together with the synergistic effect of extruding-drag-emulsification, significantly improved the oil washing efficiency. The slim tube experiment determined that the minimum miscibility pressure of CO₂ was 23.6 MPa. The plugging performance test showed that the gas-phase plugging rate of the SDBS foam system reached 95.7%, and the injection pressure difference was increased by 23.4 times. In the core displacement experiment, the total recovery rate for the low-permeability core （50×10^-3 μm²） was increased to 28.1%, and for the high-permeability core （10×10^-3 μm²） a total recovery rate of 61.4% was achieved even under the condition of a water cut of 98.3%. This study might provide theoretical basis and data support for efficient channeling plugging in oil reservoirs and for foam flooding technology.

Key words: foam system for channeling sealing, oil-based foam, surfactant, plugging performance, oil displacement mechanism, recovery rate