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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]

• 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]

Abundant oxygen-containing functional groups make lignite high moisture content, which reduces the utilization efficiency of lignite. The decrease in hydrophilicity of lignite surface can be achieved by treating with surfactant. In the present work, two kinds of nonionic surfactants with different hydrophilic groups, n-dodecyl β-D-maltoside (C 12 G 2 ) and dodecyl hepta glycol (C 12 E 7 ), were selected to modify the wettability of lignite surface by molecular dynamics simulation. Because of the drastic differences in compositions and structure of their headgroups, different behaviors were observed. The adsorption results of simulation indicate that polyhydroxy surfactant, C 12 G 2 , adsorbs strongly on lignite surface as a comparison to the poly ether surfactant, C 12 E 7 . However, the extent of hydrophobicity of modified lignite surface by these surfactants is inconsistent with their adsorption capabilities. Compared to the raw lignite, the hydrophilicity of lignite significantly decreases by adsorption of C 12 E 7 , while the C 12 G 2 makes the lignite even more hydrophilicity. The strong polar oxygen-containing functional groups of lignite surface are covered by ethers in C 12 E 7 with weaker polarity, which weakens the interaction between water and lignite. The hydrophilicity of lignite adsorbed C 12 G 2 is strengthened due to the increase in surface polarity by the introduction of polar hydroxyl groups. The results of simulations are in accord with the available experimental data. [ABSTRACT FROM AUTHOR]

Lignite is an important and useful fossil fuel in the world and the strong hydrophilicity of it limits its applications. Surfactant adsorption on lignite is an effective way to make it hydrophobic. In this work, aiming to examine the effect of the degree of ethoxylation on the adsorption behavior of dodecyl poly ethoxylated surfactants on lignite and the wettability modification of modified lignite by surfactant adsorption, different combined systems formed by surfactants, water and a model surface of Wender lignite have been studied using molecular dynamics simulation. The adsorption configurations vary with the degree of ethoxylation. At the same adsorption amounts, increasing the degree of ethoxylation can make the adsorption layer more compactness and bring stronger adsorption strength. The results of binding energy and its components show that the adsorption of alkyl polyoxyethylene ethers surfactant on lignite is physically adsorbed rather than electrostatically or chemisorbed. Meanwhile, van der Waals interaction plays a dominant role in the adsorption. The addition of surfactant could reduce the possibility of the interaction between water and lignite. Compared to the original lignite, the interaction between them is weakened after surfactant adsorption in water/surfactant/lignite system, thus strengthening the hydrophobicity of lignite. Similar to the adsorption strength, hydrophobicity of modified lignite increases with the increase of the degree of ethoxylation. The lignite surface properties are changed due to surfactant adsorption by analyzing the compositions of interaction energy and the change of hydrogen bonds. [ABSTRACT FROM AUTHOR]

Reducing coal dust is critical for environmental protection and energy efficiency, however anthracite has a high degree of coalification, high hydrophobicity, resulting in a poor dust removal effect. The addition of surfactants to water can improve the wetting of coal dust, resulting in a more effective dust reduction effect. In this investigation, Polyethylene glycol octyl phenyl ether (Triton X-100) and The lauryl polyoxyethylene ethers (C 12 (EO) 9) were chosen as research subjects. Contact angle experience, Fourier Transform infrared spectroscopy experience (FTIR), and X-ray Photoelectron Spectroscopy experience (XPS) were used to compare the ability of two surfactants to improve the wettability of anthracite from a macro perspective. Molecular dynamics (MD) simulation was used to explain macroscopic experimental phenomena from a microscopic perspective. Due to the presence of the benzene ring structure in the hydrophobic group, the surface of anthracite following Triton X-100 adsorption is more hydrophilic. The network structure of Triton X-100 molecules on the surface of anthracite is loose owing to the presence of the benzene ring, which facilitates water molecule penetration. [Display omitted] [ABSTRACT FROM AUTHOR]

External fluid invading into reservoir could induce formation damage in form of phase trapping in tight sandstone reservoirs (in-situ permeability<0.1 mD). Aqueous phase trapping damage occurs commonly in drilling and completion operations. Once aqueous phase trapping damage happens, it could hardly be removed, as a result of which gas production will not be promising. The objective of this study is to experimentally investigate the wettability alteration by quaternary ammonium fluoride salt and its potential to mitigate aqueous phase trapping damage in original water-wet, tight sandstone gas reservoirs. Wettability alteration from water wetting to gas wetting was achieved as water contact angles on core chip surface treated by 0.1 wt% fluoride were larger than 90° at 27 °C. There was hardly change in contact angles when temperature rose up to 80 °C and 100 °C respectively. The results of contact angle and surface tension tests indicated that the optimal fluoride concentration is 0.1 wt%. Atomic Force Microscope (AFM) analysis revealed that large amounts of fluoride adsorbed on mica surface, forming an irregular micro-nanometer structure. The modified structure enhanced hydrophobicity of surface and promoted the flowback of the invading fluid foreign to reservoir. Fluid rheology tests were carried out by viscometer and the results showed good compatibility between fluoride and drill-in fluid. The result of the core flow test indicated that both the flow back rate and gas relative permeability were significantly improved by 40% and 20% respectively. [ABSTRACT FROM AUTHOR]

Wettability alteration has a positive impact on mitigating the damage caused by water trapping. However, the related mechanisms are not quite clear. In this paper, the use of a quaternary ammonium fluoride salt to alter wettability and its potential to mitigate damage caused by aqueous phase trapping in the original water-wet, tight sandstone was investigated. Wettability alteration from water wetting to gas wetting was achieved after the core samples were treated with fluoride. After treatment, the water contact angles were larger than 90°. These contact angles slightly decreased when the temperature rose to 80 °C and 100 °C. The water surface tension decreased from 71.8 mN/m to 20.7 mN/m with the addition of fluoride and later varied over a small range. The contact angles and surface tension tests indicated that the optimal fluoride concentration was 0.1 wt%. The addition of fluoride slightly increased the viscous shear of the drill-in fluid. The flow back rate of the invading liquid with fluoride (85.1%) was almost double that of the liquid without fluoride (45.2%). With the removal of more water, the gas permeability recovery of cores after the circulation of drill-in fluids with fluoride improved by 20%–30% compared with that of drill-in fluids without fluoride. High performance liquid chromatography (HPLC) tests showed that there was hardly fluoride in the filtrate. The results confirmed that fluoride adsorbed onto the rock when the fluid circulated through the sample. This phenomenon was also proved by scanning electron microscopy (SEM) analysis, which showed that uneven molecular aggregation and amounts of adsorptions were more likely to occur at defect points. The adsorption of fluoride onto the rock surface resulted in a new irregular microstructure with a lower surface free energy, which decreased from 72 mJ/m 2 to 12 mJ/m 2 after fluoride adsorption. The results showed that the modified structure favors water removal. [ABSTRACT FROM AUTHOR]

Numerous core-flooding experiments have shown that low-salinity water flooding (LSWF) could improve oil recovery in sandstone reservoirs. However, LSWF recovery effects remain highly contentious primarily because of the absence of crucial boundary conditions (boundary conditions are defined throughout the paper as the initial and final, contact angle and interfacial tension values). The objective of this paper is to conduct a parametric study using statistical analysis and simulation to measure the sensitivities of LSWF recovery effects in sandstone reservoirs. The summary of 411 core-flooding experiments discussed in this paper highlights the extent and consistency in reporting boundary conditions, which has two implications for statistical analysis: (1) the statistical correlations of the residual oil saturation to chlorite (0.7891) are strong, whereas the statistical correlations of the residual oil saturation to kaolinite (0.4399) contents, as well as to the wettability index (0.3890), are comparably lower, the majority of dataset entries are missing, and no prediction model can be generated; (2) if a prediction model is generated without clay content values and a wettability index, even though LSWF effects emphasizes wettability modification by virtue of oil aging time and the strong influence of brine cation and divalent ion concentrations on Sor, the prediction model's regression curve and confidence level are poor. Reservoir simulations conducted to examine LSWF recovery sensitivities conclude that LSWF recovery effects are governed based on the initial and final wetting states. In all wetting states except for weak water-wet conditions, the increase in oil relative permeability is the underlining recovery effect. In weak water-wet conditions, LSWF incremental recovery is driven by low capillary pressures. In weak oil-wet conditions, the secondary LSWF recovery effect is the change of the non-wetting phase to oil. In all wetting states, an appreciable decrease in interfacial tension (IFT) is realized at the breakthrough recovery. The decrease in IFT is the primary recovery effect in strong water-wet conditions. [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]

Reduce the rate of acid-rock reaction is a key problem in the acidizing field. In order to reduce the damage of adsorption of traditional gelled acid in carbonate porous media, and further reduce its damage to permeability of dense carbonate rock after stimulation. Cationic surfactants can change the surface properties of rocks and control the contact area between H+ and rock surface. In order to explore the effect of different carbon chain lengths of cationic surfactants on retarding properties of acid-rock reaction, the critical micelle concentration(C cmc) and critical surface tension value(γ cmc) of seven different carbon chain lengths of cationic surfactants are determined. The results indicate that C cmc decreases significantly with the increasing of carbon chain length. The adsorption morphology of C n TAC(n = 8,10,12,14,16,18,22) species at the solid-solution interfaces is dominated by monolayer. On negatively charged calcite surface, a large number of cationic species RNH 3 + can easily adsorb on abundant CO 3 2− sites, which causes a significant increase of zeta potential for calcite. Meanwhile, the wettability of hydrophilic solid surface is modified from strongly hydrophilic to weakly hydrophilic after adsorption to control the surface rate of acid-rock reaction. The acid solution with a concentration of 1.02 × 10−2 mol/L C 14 TAC has the best retarded performance which the retardation rate is 71.01%. This research is helpful to understand the retarding performance of surfactant, improving the retarded acid system and the effect of carbonate reservoir stimulation. • The ability of different carbon-chain lengths surfactants to modify the rock surface is different. • Longer carbon chain length results in the adsorption morphology change from upright to oblique. • C12 indicates the best retarding effect and lead to the non-uniform etching of rock surface. [ABSTRACT FROM AUTHOR]