Role of Ionic Headgroups on the Thermal, Rheological, and Foaming Properties of Novel Betaine-Based Polyoxyethylene Zwitterionic Surfactants for Enhanced Oil Recovery

Long-Term Thermal Stability of Ionic Surfactants for Improving Oil Production at High-Salinity High-Temperature Conditions

Surfactants with stable chemical structures and robust ability are required to lower interfacial tension and stabilize emulsions for successful chemical injection applications. This work selected six surfactants, dodecyl carboxylic sodium (LAS), dodecyl sulfonate dodecyl sodium (SLS), dodecyl sulfate sodium (SDS), dodecyltrimethylammonium bromide (DTAB), 3-(N,N-dimethylmyristylammonio) propanesulfonate (SB3-14) and a sulfobetaine formulation (PCT-10), and systematically investigated the ionic-type effects on thermal stability at 95 °C for 150 days in high-salinity water (total dissolved solids (TDS) = 57,600 ppm). With characterizations of aged samples performed through a spinning drop tensiometer, high-performance liquid chromatography, and infrared spectroscopy, it can be seen that the long-term stability sequence of ionic surfactants in solutions is sulfobetaine ≈ quaternary ammonium > sulfonate > sulfate > carboxylate. The carboxylate possibly precipitates out from the solution in the acid form, and the sulfonate and sulfate decompositions are due to the hydrolysis of the anionic head, forming alcohol and NaHSO3/NaHSO4. Obvious decomposition of sulfobetaine and quaternary ammonium was not observed, but these molecules might suffer the elimination of the ionic head, forming the corresponding alkene and amine. The results also show that the dissolved oxygen in the solution preparation significantly sped up the degradation of sulfonates. At last, the emulsion stability tests of crude oil in surfactant solutions showed that sulfobetaine surfactants retained the highest emulsifying ability after thermal aging and thus are promising candidates for long-term chemical injection in high-temperature high-salinity reservoirs.

Synthesis of Polyether Carboxylate and the Effect of Different Electrical Properties on Its Viscosity Reduction and Emulsification of Heavy Oil

Heavy oil exploitation needs efficient viscosity reducers to reduce viscosity, and polyether carboxylate viscosity reducers have a significant viscosity reduction effect on heavy oil. Previous work has studied the effect of different side chain lengths on this viscosity reducer, and now a series of polyether carboxylate viscosity reducers, including APAD, APASD, APAS, APA, and AP5AD (the name of the viscosity reducer is determined by the name of the desired monomer), with different electrical properties have been synthesized to investigate the effect of their different electrical properties on viscosity reduction performance. Through the performance tests of surface tension, contact angle, emulsification, viscosity reduction, and foaming, it was found that APAD viscosity reducers had the best viscosity reduction performance, reducing the viscosity of heavy oil to 81 mPa·s with a viscosity reduction rate of 98.34%, and the worst viscosity reduction rate of other viscosity reducers also reached 97%. Additionally, APAD viscosity reducers have the highest emulsification rate, and the emulsion formed with heavy oil is also the most stable. The net charge of APAD was calculated from the molar ratio of the monomers and the total mass to minimize the net charge. While the net charge of other surfactants was higher. It shows that the amount of the surfactant's net charge affects the surfactant's viscosity reduction effect, and the smaller the net charge of the surfactant itself, the better the viscosity reduction effect.

Poly(Oxyethylene)-Amidoamine Based Gemini Cationic Surfactants for Oilfield Applications: Effect of Hydrophilicity of Spacer Group

Thermal stability, salt tolerance, and solubility in normal and high salinity brine are the major requirements for any surfactant designed for oilfield applications because the surfactant stays in a non-ambient environment inside the reservoir for a long period of time. Herein, a series of new gemini cationic surfactants (GSs) with varying spacer hydrophilicity were synthesized and elucidated using MALDI-ToF-MS, NMR (1H, 13C), as well as FTIR spectroscopy. GSs found to be soluble in normal as well as high salinity brine and aqueous stability tests revealed that GSs possess the ability to retain their structural integrity at high salinity and high temperature conditions because no suspension formation or precipitation was detected in the oven aged sample of GSs at 90 °C for 30 days. Thermal gravimetric analysis displayed a higher decomposition temperature than the real reservoir temperature and the GS with a secondary amine spacer exhibited high heat stability. The significant reduction in surface tension and critical micelle concentration was observed using 1 M NaCl solution in place of deionized water. The difference in surface tension and critical micelle concentration was insignificant when the 1 M NaCl solution was replaced with seawater. The synthesized surfactants can be utilized for oilfield applications in a challenging high temperature high salinity environment.