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[Display omitted] • Adsorption orientation affects the choice of optimal dust suppression surfactant. • Reversal of orientation depends on LUMO and electrostatic potential distribution. • Potential difference and hydroxyl group are the key influencing factors. • Wettability is positively correlated with adsorption orientation. Surfactants are widely used in the field of coal dust control. However, the dust suppression effect of different surfactants varies significantly, and the preferential selection mechanism of dust suppressants for mining is not clear. In this study, the water/surfactant/lignite system was constructed by molecular simulation to investigate the adsorption behavior of surfactants with different structures on the lignite surface at the molecular level. The reasons for the differences in the wettability adsorption of sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), fatty alcohol polyoxyethylene ether-9 (AEO-9), and alkyl polyglycoside (APG1214) on the lignite surface were also investigated based on the quantum chemical calculations and macroscopic experimental analysis. The results showed that the adsorption orientation of surfactant molecules at the solid–liquid interface exerted a pivotal influence on the surface wettability of lignite. According to molecular orbital and electrostatic potential analysis, surfactant molecules with LUMO distributed in the tail chain were more inclined to form a positive adsorption orientation than that concentrated in the polar headgroups; and the stronger the interaction between the polar headgroups and the coal surface with the like charge, the more stable the adsorption of surfactant molecules with the positive arrangement at the interface was. Furthermore, the stronger potential difference between SDS molecules and the hydroxyl-rich structure of the APG1214 molecules are conducive to the formation of hydrogen bonds with water molecules. Wettability experiments showed that the ability of surfactants to improve the wettability of coal dust was positively correlated with the adsorption orientation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adsorption orientation affects the choice of optimal dust suppression surfactant. • Reversal of orientation depends on LUMO and electrostatic potential distribution. • Potential difference and hydroxyl group are the key influencing factors. • Wettability is positively correlated with adsorption orientation. Surfactants are widely used in the field of coal dust control. However, the dust suppression effect of different surfactants varies significantly, and the preferential selection mechanism of dust suppressants for mining is not clear. In this study, the water/surfactant/lignite system was constructed by molecular simulation to investigate the adsorption behavior of surfactants with different structures on the lignite surface at the molecular level. The reasons for the differences in the wettability adsorption of sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), fatty alcohol polyoxyethylene ether-9 (AEO-9), and alkyl polyglycoside (APG1214) on the lignite surface were also investigated based on the quantum chemical calculations and macroscopic experimental analysis. The results showed that the adsorption orientation of surfactant molecules at the solid–liquid interface exerted a pivotal influence on the surface wettability of lignite. According to molecular orbital and electrostatic potential analysis, surfactant molecules with LUMO distributed in the tail chain were more inclined to form a positive adsorption orientation than that concentrated in the polar headgroups; and the stronger the interaction between the polar headgroups and the coal surface with the like charge, the more stable the adsorption of surfactant molecules with the positive arrangement at the interface was. Furthermore, the stronger potential difference between SDS molecules and the hydroxyl-rich structure of the APG1214 molecules are conducive to the formation of hydrogen bonds with water molecules. Wettability experiments showed that the ability of surfactants to improve the wettability of coal dust was positively correlated with the adsorption orientation. [ABSTRACT FROM AUTHOR]

• Carbonate-rich shale became more oil-wet with the increasing temperature. • Higher CTAB concentration made all the shales more oil-wet. • Higher SDS concentration made clay-/organic-rich shale more water-wet. • Higher SDS concentration had a non-monotonous effect on carbonate-rich shale. Shale wettability affects pore-scale oil/water distribution and reservoir-scale oil extraction efficiency. For enhanced oil recovery, a common method to modify rocks' wettability is adding surfactant. However, previous experiments mainly focused on room temperature conditions, which are not representative of the high-temperature conditions in shale oil reservoirs. Meanwhile, shale consists of various compositions (e.g., clay, carbonate, organic matter), and each composition is expected to have a different influence on shale wettability in a complex way. So far, a comprehensive investigation of shale wettability modification by surfactants and temperature in oil reservoir conditions is still lacking. Therefore, in this work, the effects of temperature (25 ℃ vs 50 ℃), surfactant type (Cetyltrimethylammonium bromide [CTAB] vs Sodium dodecyl sulfate [SDS]) and concentration (0 ∼ 0.2 wt%), and shale compositions (carbonate-, clay- and organic-rich) on shale wettability were investigated systematically via contact angle (θ) measurements in the water-oil-shale system. It is demonstrated that 1) as the temperature increased, the carbonate-rich shale became more oil-wet, no matter the presence or absence of surfactants, while clay- and organic-rich shale became either more oil-wet or more water-wet; 2) At high temperature (i.e., 50 ℃), higher CTAB concentration made all the shales more hydrophobic; higher SDS concentration modified clay- and organic-rich shale more hydrophilic, while had a non-monotonous influence on carbonate-rich shale; 3) At 50 ℃, clay- and organic-rich shale shifted from strongly water-wet to strongly oil-wet with the addition of CTAB, while it became more water-wet with the addition of SDS; carbonate-rich shale became more oil-wet with the addition of CTAB, while it fluctuated erratically with the addition of SDS. This research provides fundamental guidance on wettability modification via surfactant, which has promising applications in EOR in shale oil reservoirs. [ABSTRACT FROM AUTHOR]

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), hydrolyzed 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 to 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. Image 1 • Natural L-amino acids such as L-arginine, L-lysine, L-methionine and L-tryptophan were tested as an EOR agent. • L-amino acids have high salt and hardness tolerance and are stable at high temperatures. • L-amino acids reduce the interfacial tension between crude oil and water and enhance the surface activity of surfactants. • L-amino acids have great potential as wettability modifier and hence could be used as an EOR agent. • The performance of L-arginine in reducing the IFT between crude oil and water is quite close to that of SDS. [ABSTRACT FROM AUTHOR]