Insight into functional groups of salt compounds on the performance of viscoelastic surfactant-based fluids

Clean fracturing fluids (CFFs) hold great potential for the development of unconventional reservoirs due to their characteristics (e.g., fracturing-oil expulsion integration and low formation damage). Organic salts, as adjuvants, play a significant role in regulating the performance of CFFs. In this work, four CFFs containing different organic salts were prepared to investigate the impact of functional groups in organic salts on the CFF performance. Results show that the functional groups markedly influence the rheological properties, temperature resistance and drag reduction performances of CFFs through inducing the micelle formation and thus enhancing the micelle network strength. Sodium 4-vinylbenzenesulfonate (SV) with vinyl endowed the CFF with the stronger micelle network. Furthermore, the functional groups were found to impact the adsorption of surfactants at interface, which affects the oil-water interfacial tensions and regulates the spontaneous imbibition performance of CFFs. SV enables a higher imbibition efficiency of 25.6 % after 90 h. Density functional theory (DFT) calculation results confirmed that the functional groups of salts are capable of manipulating the interactions between salt anions and surfactant, ultimately determining the CFF performance. This work provides guidance for the selection of salt additives to improve the CFF performance.