A study on the thermal stability of hydroxy sulfobetaine surfactants in brine

3-(N-dodecyl-N, N-dimethyl)-2-hydroxypropyl sulfobetaine (HSB12) and 3-(N-lauramidopropyl-N, N-dimethyl)-2-hydroxypropyl sulfobetaine (LHSB) exhibit exceptional solubility and foaming performance in brine with a salinity of 22 × 10 4 mg/L. These properties render them promising candidates as foaming agents for gas mobility control in high-temperature, high-salinity oil reservoirs to enhance oil recovery. However, the precise temperature tolerance limits of these surfactants remain unclear. This study systematically investigates their thermal stability under high-temperature conditions. The results demonstrate that LHSB exhibits slightly superior foaming performance compared to HSB12 prior to heat treatment. After 7 days of thermal treatment at 130 °C, the foam stability of LHSB significantly deteriorates, whereas HSB12 maintains consistent foaming performance even after 30 days of thermal treatment. To further evaluate the thermal stability of LHSB and HSB12 in brine, a method for quantifying their concentrations using high-performance liquid chromatography (HPLC) was developed. Based on this method, systematic evaluations were conducted regarding the changes in LHSB and HSB12 concentrations following long-term heat treatment at 110 °C, 130 °C, and 150 °C. The findings reveal that LHSB exhibits excellent long-term thermal stability at 110 °C, while HSB12 demonstrates comparable stability at 130 °C. Therefore, it is recommended that LHSB be utilized as the foaming agent for oil reservoirs operating at 110 °C and HSB12 for reservoirs functioning within the 130–150 °C range. Additionally, LC-MS analysis confirms that LHSB is susceptible to amide bond hydrolysis and C-N bond cleavage between propyl groups and quaternary nitrogen at high temperatures. These results provide valuable insights into the scientific application of LHSB and HSB12 in high-temperature, high-salinity reservoirs. The standard curves of LHSB and HSB12, along with their content retention following thermal treatment at various temperatures and durations, were determined using liquid chromatography (HPLC)