Chemical Enhanced Oil Recovery from Carbonate Reservoirs by Coherent Surfactant and Surfactant–Alkali (SA) Slug Injection Using a Green Cationic..

Natural surfactants are proposed as alternatives to chemical surfactants in enhanced oil recovery (EOR) process. This research involved the synthesis and analysis of a new green cationic surfactant extracted from avocado oil. We studied the properties of the surfactant solutions by conducting tests on the surface tension, emulsion formation, and compatibility with varying levels of salinity. After that, in order to study the efficiency of the surfactant, rudimentary tests of EOR, including surface and interfacial tension (IFT), contact angle, adsorption in porous medium, and two injection schemes of coherent surfactant and surfactant–alkali (SA) slug, were performed. The main functional groups in the avocado oil cationic surfactant (AOCS) include amide, amine, and sulfate groups, which were confirmed by related analyses. The estimated critical micelle concentration (CMC) of the avocado oil-based cationic surfactant (AOCS) was found to be approximately 725 ± 25 ppm (ppm). At this concentration, the interfacial tension between the surfactant and the oil surrounding medium was measured to be 0.316 millinewtons per meter (mN/m). Furthermore, the interfacial tension decreased to 0.063 and 0.035 mN/m under optimal salinity and alkalinity, respectively. The value of interfacial tension after about 35 days of the solution’s shelf life was out of the desired range. The contact angle decreased from 126.81 to 61.53° after 180 min, and the wettability of carbonate altered from oleophilic to hydrophilic by the surfactant. The AOCS was compatible with up to 60,000 ppm salinity, and after the injection of 2.5 PV, 6.2 wt % of it was adsorbed on the carbonate. The coherent injection of the AOCS increased the oil recovery by 25.6% to a total recovery of 80.1%. In another method, injecting a slug of SA with a volume equal to 0.5 pore volumes (PV) resulted in a significant increase in oil recovery, amounting to a 23.4% improvement, and the total recovery reached 77.7%.