Design and Synthesis of Pyridinium-Based Zwitterionic Surfactants for Oilfield Applications: Structure-Performance...

The primary characteristics to be considered for potential oilfield application of surfactants are solubility and thermal stability. One significant challenge for surfactants that are currently available in the market is hydrolysis at high temperatures, which is accelerated by continued heating. Herein, six pyridinium-based zwitterionic surfactants were synthesized, including three fluorinated surfactants and three hydrocarbon surfactants. The influence of chain length was studied and a comparative study of fluoro versus hydrocarbon surfactants on salt tolerance, thermal, and surface properties was conducted. All six surfactants exhibited remarkable solubility and stability in water, including deionized water, seawater (SW), and formation water. Furthermore, the surfactant solution remained transparent after being kept at 90 °C for 1 week with no sign of cloudiness or precipitation. However, the F₉APC was visually observed to be slightly cloudy after aging for 1 week in FW; this qualitative observation did not affect its filterability. This can be linked to the higher number of fluorine atoms, which increases hydrophobicity. The thermal gravimetric analysis thermograms show that all newly synthesized zwitterionic surfactants decompose at more than 250 °C, substantially greater than the oilfield temperature. The fluoro-based surfactants have lower critical micelle concentration (CMC) and surface tension values compared to hydrocarbon-based surfactants. The lower CMC value of long-tailed fluorinated surfactants indicates that they can form a more tightly packed micelle compared to hydrocarbon tail-based surfactants. These unique characteristics, including thermal and surface properties, make them ideal surfactants for harsh reservoir environments.