(181bg) Performance Evaluation of Synthesized Gemini Cationic Surfactants Having Different Hydrophobic Tail and Spacer Length for Enhanced Oil Recovery

Commercial surfactants such as alkyl benzyl sulfonate, petroleum sulfonate, and polyoxyethylene ether suffer due to stability issues when applying in high salinity (120,000-220,000 ppm) and high temperature (≥90^oC) carbonate reservoir. The harsh environment of reservoir causes surfactant decomposition and decrease their performance in lowering interfacial tension (IFT), altering rocks wettability, and mobilization.

For addressing surfactant stability issues, range of gemini cationic surfactants were prepared having different hydrophobic tail and spacer groups. The chemical structures were confirmed with the aid of NMR (¹H, ¹³C), FTIR, and mass analysis. The solubility tests were conducted in deionized water (DW) as well as simulated sea water (SW) and formation brine (FW). Heat stability was assessed using Thermal Gravimetric Analysis (TGA) and aging methods. The spinning drop method was used to identify interfacial tension. The critical micelle concentration (cmc) as well as surface tension at cmc was measured with the aid of Force tensiometer (Biolin Scientific). The rheology of surfactant/polymer hybrid was performed on discovery hybrid rheometer (DHR-3).

The surfactants exhibited good solubility in DW, SW, and FW and no phase separation or precipitation was detected. According to TGA graph, the decomposition temperature of the prepared surfactants was higher than 250 ^oC which is superior to oilfield temperature (≥90^oC). Similarly, the aging technique revealed no change in chemical structure after putting them in oven at 90 ^oC for 3 months. The cmc, surface tension at cmc, and interfacial tension of the surfactants was comparable or superior to the industrially applied surfactants. According to rheological data, the surfactant found to be compatible with the polymer and the storage modulus was decreased upon increasing the surfactant concentration at lower rate of shear and frequency because of charge screening and surfactant-polymer interaction.

The developed gemini cationic surfactants exhibited remarkable heat stability and salt tolerance and demonstrated big potential in harsh carbonate rocks in which anionic surfactants are not suggested because of large adsorption.