Influence of Lipophilic Tail and Lipophobic Spacer on the Thermal and Surface Properties of the Synthesized Gemini Surfactants for Enhanced Oil Recovery

The temperature range of carbonate reservoir is almost 100 ^oC and the salinity touches 220,000 ppm. Surfactants are known to minimize interfacial tension and promote wettability change. The heat stability and aqueous solubility of the surfactants for enhanced oil recovery application is the major concern. The developed surfactant must be thermally stable and tolerant to reservoir ions.

For this purpose, several gemini cationic surfactants containing different lipophilic tail and spacer groups were synthesized. The NMR, FTIR, and MALDI-TOF MS techniques were used to identify chemical structure of the gemini surfactants. Thermal gravimetric analysis as well as aging methods was utilized to investigate short and long time heat stabilities. Surface tension was studied through pendant drop technique and the interfacial tension was examined by spinning drop method. Rheological properties were elucidated with the help of discovery hybrid rheometer (DHR-3).

The locally produced gemini surfactants showed excellent short range and long range heat stabilities. The incorporation of glycolic groups in surfactant tail leads to better solubility of the gemini surfactants in formation brine (220,000 ppm). The critical micelle concentration, the related surface tension, and the interfacial tension values were comparable or higher to the industrially applied surfactants. The rheological data exhibited that the storage modulus was decreased by enhancing surfactant concentration at lower shear and frequency due to chemical interaction and charge screening.

The synthesized gemini surfactants exposed better salt tolerance and heat stabilities and demonstrated great potential in high-salinity high-temperature carbonate reservoirs.