Influence of natural L-amino acids on the interfacial tension of an oil-water system and rock wettability alterations

Abstract

Abstract The cost and environmental effects of most conventional surfactants have increased the search for a greener and cheaper alternative for enhanced oil recovery (EOR) applications. The natural L-amino acids are amphoteric compound with excellent surface properties that have found versatile applications in the pharmaceutical, cosmetic, and food industries. These amino acids exhibited amphipathic nature due to their hydrophobic alkyl chain and charged head. Hence, they could form contacts with both polar and non-polar surface ligands simultaneously. In this study, four amino acids, namely L-arginine, L-lysine, L-methionine, and L-tryptophan, were investigated to access their ability to reduce the interfacial tension (IFT) and alter the wettability of oil-wet sandstone rock. The pendant/rising drop and sessile drop method were employed in IFT and contact angle measurements. The stability of amino acids in brine and the compatibility with other EOR chemicals were tested through visual observation of the precipitates and cloudiness. With the exception of L-tryptophan, the compatibility and stability results revealed that all the amino acids have high salt tolerance above 25 wt.% sodium chloride (NaCl). The solutions of amino acids and chemicals such as cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), hydrolysed polyacrylamide (HPAM), alkali, and alkali-polymer were transparent even at 80 °C. The IFT test results showed that the amino acids significantly reduced the crude oil-water IFT compared to the IFT of n-decane-water system. The IFT between deionized water and crude oil decreased by 76.61% and 55.24%, 24.79%, 45.23% in the presence of L-arginine, lysine, methionine, and tryptophan solutions, respectively. Addition of 0.01 wt.% L-arginine, L-lysine and L-methionine to 0.1 wt% SDS reduced the IFT by 28.3 %, 15.6 %, and 10.97 % respectively. The contact angle test showed that L-amino acids have great potential as wettability modifying agents. The contact angles reduced with the decreasing pH (potential of hydrogen) and with increasing brine concentrations from 1-4 wt.%. Specifically, the contact angle reduced from 92.3°, 91.42°, 89.81° and 92.95 to 47.24°, 53.9°, 58.9° and 59.0° for L-arginine, L-lysine, L-methionine and L-tryptophan, respectively at a pH of about 3. The study suggests that the L-amino acids could be a potential EOR agent in a high saline environment, mainly as a wettability modifier, as well as additives to improve the surface activity of the conventional surfactant and EOR chemicals.