Screening and Optimization of Surfactant for N2-Foam Stabilization in Carbonates under Harsh Conditions

  • Ding Xiong

    Student thesis: Master's Thesis

    Abstract

    Foam injection is designed to improve gas sweep efficiency through reducing the adverse effects of channeling through high heterogeneities occurring in reservoirs as well as gravity override and viscous fingering problems. However, harsh reservoir conditions in the Middle East carbonate reservoirs pose severe problems to foam stability, leading to poor mobility control for foam injection. In this study, different surfactant types were tested to screen and optimize foam performance in carbonates under high salinity, high temperature, and high pressure conditions based on series of bulk foam and coreflooding experiments. Different commercial amphoteric and amine-based switchable surfactants were evaluated at high salinity brine (20 wt% NaCl) and high temperature conditions (80 ℃). Initial screening studies were conducted using air-foam including series of foam stability and foamability tests at high temperature. Surface tension and aqueous solution rheology were also tested to analyze the foam behavior. Foam generation and endurance were investigated. After determining the optimal single surfactant performance, surfactant mixtures containing amphoteric and switchable surfactants were then investigated to check the foam performance in the presence and absence of crude oil. A pressurized foam cell was used to study the characteristics of foam stability and foam texture at different foam qualities under reservoir conditions at the bubble scale. On the other hand, at the core-scale, the performance of nitrogen-foam was evaluated in carbonate outcrop samples at different foam qualities and flow rates under reservoir conditions without the presence of oil. After selecting the optimal foam quality that ensures an effective foam generation, a tertiary foam oil recovery experiment was conducted targeting the remaining oil after the secondary nitrogen-gas flood. Bulk foam experiments at a high temperature and high salinity concluded that betaine surfactant (B-1235) resulted in the highest foam generation and foam stability among other tested surfactants. The betaine foam endurance was similar to the foam produced by the viscoelastic diamine surfactant (Duomeen TTM). However, the latter surfactant was excluded due to the lowest foam generation performance. Foaming results with crude oil indicated that only B-1235 surfactant could maintain its foam properties compared to other surfactants used. The optimum concentrations of the betaine surfactant in the absence and presence of crude oil were found to be 0.25 and 0.5 wt%, respectively. A mixture of B-1235 surfactant and the amine-based surfactant (Ethomeen C/12) enhanced the foam performance of any individual surfactant without oil presence. Nevertheless, in the presence of crude oil, the foam performance of surfactant mixtures was not as good as the single betaine surfactant. The foam generated by co-injecting B-1235 and air pronouncedly increased the half-life at all tested foam qualities under the pressurized foam cell, and a foam quality of 90% was determined at bubble scale providing the finest foam texture and highest foam stability. One the other hand, coreflood investigation indicated an optimal foam quality of 70% for both 0.25 and 0.5 wt% surfactant concentrations, and a shear-thinning behavior was confirmed as the flow rates were varied. The optimum foam was able to provide a pronounced incremental oil recovery of 25% OOIP after the secondary nitrogen flood. This study is among the very few that discusses the potential of amphoteric surfactants as foaming agents in carbonates under harsh conditions of high temperature and high salinity. The findings of this study encourage field scale implementation of this technique in mature waterflooded carbonate reservoirs in the Middle East region.
    Date of AwardDec 2021
    Original languageAmerican English

    Keywords

    • Foam Stability; Amphoteric Surfactant; Switchable Surfactant; Surfactant Mixture; Foam Texture; Harsh Reservoir Conditions.

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