Probing high-salinity-enhanced stability of betaine foam for foam application in harsh reservoirs

The stability of betaine foam can be enhanced by salts in reservoirs, even with salinity as high as 2 × 10⁵ mg/L, which offers great potential for cost-effectively improving the foam performance in high-salinity reservoirs. There is, however, a lack of understanding of the mechanisms behind this behavior. This study focused on the surface and bulk phase properties of three betaines with alkyl chain lengths of C₁₂–C₂₁ to probe the mechanisms leading to the high-salinity-enhanced foam stability. The dilatational viscoelasticity, adsorption behavior, surface relaxation, rheology, and thin-film drainage were examined in a wide NaCl range of 2.3 × 10⁴ to 2.1 × 10⁵ mg/L. With increasing salinity, betaine molecules adsorbed on the gas–water surface increased, and molecule diffusion–exchange between the surface and bulk phase decelerated, resulting in increased dilatational moduli and surface elasticity. The enhanced dilatational viscoelasticity slowed coarsening and coalescence, thus promoting the stability of betaine foam. The foam generated by oleicyl dimethyl amidopropyl carboxybetaine exhibited much stronger stability than the other betaine foams, especially when the NaCl concentration approached 2.1 × 10⁵ mg/L. The viscoelastic micelle induced by high salinity dominated its superior stability.