Enhancing scale inhibitor squeeze lifecycle in a carbonate reservoir

  • Xin Li

    Student thesis: Master's Thesis

    Abstract

    Precipitation of inorganic scale in produced water and their deposition in the oil and gas well tubular and near wellbore formation could be a huge disadvantage in terms of well productivity and operational expenditure. To mitigate such problem, scale inhibitor squeeze treatment is an established method, having numerous successful lab-scale and field-scale applications. Since inorganic scale is built up in water solution, most of scale inhibitor chemicals are water soluble and typically deployed as an aqueous phase. However, aqueous based treatment may not perform very well in limestone reservoir, if it is mixed-wet or oil-wet type, as it would be very difficult for scale inhibiting chemicals to be adsorbed onto the oil-wet rock surface. Even if the pore surface is partially water wet, a portion of the pore surface will be covered with oil, which will deprive the scale inhibitor a significant fraction of the pore surface for adsorption. Reduced adsorption leads to reduced scale inhibitor squeeze life time, which demands frequent treatment, leading to increased OPEX and production interruption. Once this phenomenon is realized, it is essential to create a clean and suitable pore surface prior to the scale inhibitor squeeze. In this study our objective was to alter the wettability in carbonate reservoirs to a favorable direction (towards more water wet), drive out the remaining oil in the near wellbore formation to be treated with the help of a suitable surfactant formulation and also to remove the adsorbed surfactant from the pore surfaces to provide a clean and water wet surface for maximum scale inhibitor adsorption. In a traditional SI squeeze strategy, a surfactant preflush is generally used to clean formation before SI main treatment. Surfactant preflush can effectively remove the oil out from the oil-wet rock surface by lowering interfacial tension (IFT) between oil and preflush. However, different types and concentrations of surfactant can give different performance. Since carbonate rock surfaces are usually positively charged and oil in most cases is negatively charged, anionic surfactant can't effectively clean oil, while cationic surfactant and nonionic surfactant can perform better in terms of lowering IFT due to their attraction to oil. To create a cleaner surface and improve SI adsorption, several squeeze strategies are designed. Amott-Harvey test and Flotation test are conducted to examine the wettability of different core plugs before and after surfactant treatment. Meanwhile, interfacial tension between oil sample and surfactant with or without alkalis, of different concentrations are studied to optimize surfactant formulation. Finally, coreflooding experiments are performed to determine and compare squeeze lifetime of SI under different designed strategies. The results show that optimized surfactant-alkali preflush is able to alter the wettability towards more water-wetness. Moreover, nonionic surfactant shows better performance than anionic surfactant and cationic surfactant because of its neutral surface charge. Sodium carbonate is quite effective at cleaning adsorbed surfactant, therefore further enhancing water-wet tendency. Correspondingly, the squeeze lifetime is extended to varying extent according to the level of water wetness. The maximum squeeze lifetime achieved is 2026 pore volumes of produced compared to the industry practice (benchmark) which is just 826 pore volumes. Thus the modified method increased squeeze lifetime by 147.7%. This study will provide good reference for future squeeze treatment design in carbonate reservoir for full field scale inhibitor applications.
    Date of Award2011
    Original languageAmerican English
    SupervisorBisweswar Ghosh (Supervisor)

    Keywords

    • Applied sciences
    • Carbonate reservoirs
    • Petroleum engineering
    • Energy.

    Cite this

    '