Synergistic performance of an in-house synthesized cationic Gemini surfactant for enhanced oil recovery under harsh conditions

Surfactant injection into hydrocarbon reservoirs is a proven method for enhanced oil recovery, leveraging its ability to reduce interfacial tension between oil and water and potentially alter rock wettability. This study investigates the effectiveness of integrating various additives/methods, including brackish water, DTPA, or methylene blue, into the oil recovery process using a modified cationic Gemini surfactant (GS8), particularly in challenging conditions. Four coreflooding experiments were carried out in Indiana limestone cores at 100 ℃, each involving continuous injection of a chemical solution following continuous injection brine flooding. The solutions were either the surfactant in the injection brine, the surfactant in brackish water, the surfactant in injection brine with 1 wt% DTPA, or the surfactant in injection brine with 300 ppm methylene blue, all at a constant surfactant concentration of 2,500 ppm. The injection-brine-flood phase yielded oil recovery ranging from 46 % to 49 % of the original oil in place and residual oil saturations between 33 % and 35.5 %. The GS8-in-injection-brine and the GS8-in-brackish-water floods produced incremental oil recoveries of 23 % and 26.3 % OOIP, respectively. The surfactant's dynamic retentions were 0.37 and 0.35 mg/g-rock, respectively. Incorporating DTPA into the recovery process led to the largest additional oil recovery among all tested solutions at approximately 37 % OOIP, resulting in an ultimate oil recovery of 84 % OOIP with a dynamic retention of 0.41 mg/g-rock. However, adding methylene blue with the GS8 slowed down the recovery process, requiring a larger volume of chemical solution. Overall, the study highlights the synergistic effects of combining the surfactant with different base fluids to optimize oil recovery while maintaining low surfactant retention. This study also explores strategies for optimizing surfactant flooding, intending to advance sustainable chemical flooding practices.