Title : Lessons for field-specific approach in addressing polymer stabilized O/W Emulsions: Insights from EOR in indian onshore field
Abstract:
MBA field in Indian Western Onshore Basin has been implementing large-scale polymer flooding with hydrolyzed polyacrylamide (HPAM) since 2015. Polymer flooding (PF) is being carried out by injecting ~500,000 bpd water with ~165 tpd of HPAM. PF has successfully slowed production decline and is projected to yield ~8% incremental oil recovery (~100 million barrels) by 2030. A significant operational challenge observed over time is formation of stable oil-in-water(O/W) emulsions in the near-wellbore region with injected water having high oil content (300-700 ppm); primarily due to high paraffinic content of the crude oil (with WAT very close to reservoir temperatures), and the presence of residual HPAM in the injected water. This study investigates the mechanisms behind emulsion stabilization, evaluates the effectiveness of various demulsification methodologies and proposes optimized formulations to restore well injectivity and improve EOR efficiency. A comprehensive laboratory study was conducted to analyze the formation, stabilization and resolution of O/W emulsions at reservoir temperatures. High frequency ultrasonication was used to form stable O/W emulsions. Emulsions were further characterized by microscopic imaging. Demulsification efficiency of various surfactant based formulations was assessed both qualitatively and quantitatively with bottle testing, microscopic imaging, turbidity analysis and zeta potential measurements. Turbidity and zeta potential analysis were further utilized to assess demulsification performance with varying dosage of surfactants. Residual HPAM was identified as a key stabilizing agent in O/W emulsions, with probable formation of a protective interfacial layer around dispersed oil droplets. While literature has referenced to dominant use of cationic surfactants for resolving O/W emulsions, our results demonstrated their ineffectiveness for O/W emulsions stabilized by high polymer concentrations and instead opaque viscous emulsions were generated. Nonionic surfactants showed moderate demulsification efficiency and high sensitivity to overdosing, indicating the risk of secondary emulsion restabilization. An optimized combination of amphoteric and nonionic surfactants achieved high demulsification efficiency (>95%), as confirmed through turbidity and zeta potential analysis. Figure 1 shows O/W emulsions with E1 as blank emulsion(E), E2 as E+cationic surfactant, E3 as E+anionic surfactant, E4 as E+amphoteric surfactant, E5 having E+non-ionic surfactant with emulsion resolution observed in E4 and E5.Additionally, this formulation demonstrated lower sensitivity to dosage variations, minimizing the risk of emulsion restabilization. The study underscores the necessity of a tailored, reservoir-specific demulsification approach over one-size-fits-all approach, as generic solutions may exacerbate challenges instead of resolution.
