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The development of combinatory flooding has evolved over the years to utilize the synergies that come into play upon combining more than one chemical agent in a chemical flooding process. This study focuses on investigating the synergies that exist in combining monoethanolamine (ETA) and sodium cocoyl alaninate (SCA) as an alkali–surfactant (AS) formulation for the enhanced oil recovery process. A conventional formulation made of sodium carbonate (Na2CO3) and sodium dodecyl sulfate (SDS) was used for a comparative purpose. The proposed formulation proved to be compatible with the prepared hard brine. The ETA–SCA combination proved superior to Na2CO3–SDS in interfacial tension (IFT) reduction and wettability alteration. Addition of ETA to SCA synergistically reduced IFT to a low value of 4.73 × 10–2 mN/m at a surfactant concentration lower than the critical micelle concentration (CMC). ETA also played a synergistic role in improving the wetting power of SCA on quartz surface. The formulation also showed a high emulsifying ability owing to its superior IFT reduction capability. Static adsorption studies showed SCA to exhibit Langmuir-type adsorption behavior similar to SDS. The adsorption of SCA onto a sand surface was favorable, but ETA proved to reduce adsorption of SCA effectively at 0.3 wt %. The ETA–SCA and Na2CO3–SDS systems achieved additional oil recoveries of 31 and 25% original oil in place (OOIP) over conventional core flooding, respectively. The proposed AS formulation, therefore, showed better recovery potential in addition to its environmentally friendly nature.

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Combinatory flooding techniques evolved over the years to mitigate various limitations associated with unitary flooding techniques and to enhance their performance as well. This study investigates the potential of a combination of 1-hexadecyl-3-methyl imidazolium bromide (C16mimBr) and monoethanolamine (ETA) as an alkali–surfactant (AS) formulation for enhanced oil recovery. The study is conducted comparative to a conventional combination of cetyltrimethylammonium bromide (CTAB) and sodium metaborate (NaBO2). The study confirmed that C16mimBr and CTAB have similar aggregation behaviors and surface activities. The ETA–C16mimBr system proved to be compatible with brine containing an appreciable concentration of divalent cations. Studies on interfacial properties showed that the ETA–C16mimBr system exhibited an improved IFT reduction capability better than the NaBO2–CTAB system, attaining an ultra-low IFT of 7.6 × 10−3 mN/m. The IFT reduction performance of the ETA–C16mimBr system was improved in the presence of salt, attaining an ultra-low IFT of 2.3 × 10−3 mN/m. The system also maintained an ultra-low IFT even in high salinity conditions of 15 wt% NaCl concentration. Synergism was evident for the ETA–C16mimBr system also in altering the carbonate rock surface, while the wetting power of CTAB was not improved by the addition of NaBO2. Both the ETA–C16mimBr and NaBO2–CTAB systems proved to form stable emulsions even at elevated temperatures. This study, therefore, reveals that a combination of surface-active ionic liquid and organic alkali has excellent potential in enhancing the oil recovery in carbonate reservoirs at high salinity, high-temperature conditions in carbonate formations.

Amino acid-based surfactants (AASs) and other novel surfactants have recently gained attention to provide a favorable environmental image (“green”) in surfactant application. Yet their potential in enhancing oil recovery is not well investigated. Only a few works have been reported on their potential enhanced oil recovery (EOR) application with less satisfactory results. Here in, sodium cocoyl alaninate (SCA), an acylated amino acid with excellent properties that facilitate its application in other fields, is investigated for its EOR potential. Its effectiveness in lowering the interfacial tension and the emulsifying crude oil–brine mixture were studied. The ability to alter rock surface wettability and its adsorption behavior on the sand surface were studied as well. Then, its oil recovery potential was confirmed through a core displacement experiment. All studies were performed in comparison with conventionally deployed sodium dodecyl sulfate (SDS). The critical micelle concentrations for SCA (CMC = 0.23 wt%) and SDS (CMC = 0.21 wt%) were close, which serves as a good basis for comparing their EOR potential. SCA proved to be more effective in IFT reduction attaining a minimum IFT of 0.069 mN/m (i.e., ~ 98.8% IFT reduction) compared to 0.222 mN/m of SDS (i.e., ~ 96.2% IFT reduction) at the same concentration. Salinity showed a synergistic effect on the interfacial properties of both SCA and SDS but had a more significant impact on SDS interfacial properties than SCA due to low salt tolerance of SDS. The low IFT attained by SCA yielded enhanced emulsion formation and stable emulsion both at 25 °C and 80 °C for a period of one week. SCA also altered quartz surface wettability better via reduction of contact angle by 94.55% compared to SDS with contact angle reduction of 87.51%. The adsorption data were analyzed with the aid of various adsorption isotherm models. The adsorption behavior of SCA and SDS could be best described by the Langmuir model. This means a monomolecular surfactant layer exists at the aqueous–rock interface. SDS also exhibited more severe adsorption on the sand surface with the maximum adsorption density of 15.94 mg/g compared to SCA with the maximum adsorption density of 13.64 mg/g. The core flood data also confirmed that SCA has a better oil recovery potential than SDS with an additional oil recovery of 29.53% compared to 23.83% of SDS. This additional oil recovery was very satisfactory compared to the performance of other AAS that have been studied. This study therefore proves that SCA and other AAS could be outstanding alternatives to conventional EOR surfactants owing to their excellent EOR potential in addition to their environmental benign nature.

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