Development and Study of a Salt and Oil Tolerant Foamer System for Tight Gas Well Foam Drainage Gas Recovery

To address the technical challenge of severe performance degradation of foaming agents caused by high-salinity formation water and condensate during drainage gas recovery in tight gas wells, this study developed a composite foam system (BLZP) with excellent salt and oil tolerance. Through chemical modification, zwitterionic groups (sulfonate and quaternary ammonium) were introduced into the poly-(vinyl alcohol) (PVA) backbone to synthesize a zwitterionic polymer ZPVA, which served as a stabilizer. ZPVA was then optimized via orthogonal experiments with the zwitterionic primary foaming agent dodecyl dimethyl betaine (BS-12) and the nonionic cofoaming agent lauryl dimethyl amine oxide (LAO). Sodium perfluorononyloxybenzenesulfonate (OBS) was subsequently incorporated as an enhancer. Systematic characterization and evaluation demonstrated that ZPVA effectively suppresses polymer aggregation in 10 wt % NaCl or CaCl₂ solutions, maintaining smaller hydrodynamic sizes and higher solution viscosities. The optimized BLZP system exhibited significantly enhanced interfacial dilatational viscoelasticity in simulated high-salinity formation water (TDS 78,050 mg/L). Oil-tolerance tests (with condensate content up to 60%) further revealed that BLZP, owing to its compact and highly elastic composite interfacial adsorption layer, effectively inhibits oil droplet spreading and bridging-induced foam rupture. The decrease in initial foam height (H ₀) and 5 min foam height (H ₅) was substantially lower than that of two commercial foaming agents. Even at 60% oil content, BLZP maintained H ₅ > 150 mm, liquid carrying ratio >40%, and foam water content >4%, demonstrating outstanding potential for field applications. This study provides an innovative chemical solution for efficient foam-assisted drainage gas recovery under challenging reservoir conditions.