Dominant performance parameter and technical limits of surfactants for oil displacement

In chemical flooding, emulsification and interfacial tension (IFT) reduction are crucial for enhanced oil recovery (EOR). However, the dominant performance parameter and technical limits of surfactants for oil displacement remain underexplored. This study investigated the relationship between the emulsification capability and IFT. Accordingly, the dominant performance parameter and the technical limits of surfactants were determined using oil displacement experiments. Specifically, an analysis of 74 sets of experimental results revealed a shift in the significant correlation between EI (a quantitative measure of emulsification capability) and σ at an σ value of 8.5 × 10⁻² mN/m (i.e., critical value σ_c). For σ < σ_c, emulsification capability and IFT function as independent performance parameters. The oil displacement experiments using two surfactants with contrasting EI and σ values demonstrate that emulsification capability, rather than ultra-low IFT, is the dominant performance parameter. This study determined the technical limit of EI using oil displacement experiments via in-situ emulsification. The experimental results indicate strong correlations of EI with oil displacement and recovery efficiencies. The incremental displacement and recovery efficiencies were employed to quantify the potential of surfactants to enhance oil displacement and recovery efficiencies, respectively. The incremental displacement and recovery efficiencies versus EI curves revealed a critical EI (EI_c) value of 0.53. When EI < EI_c, the incremental displacement and recovery efficiencies increased significantly with EI. In contrast, when EI > EI_c, their increasing rates slowed down markedly. Therefore, the technical limits of the emulsification capability and IFT of surfactants used in this study are determined at EI ≥ 0.53 and σ ≤ 8.5 × 10⁻² mN/m, respectively.