Xinwang Song

Mechanisms of Enhanced Oil Recovery by Surfactant-Induced Wettability Alteration

Different measurements were conducted to study the mechanisms of enhanced oil recovery (EOR) by surfactant-induced wettability alteration. The adhesion work could be reduced by the surfactant-induced wettability alteration from oil-wet conditions to water-wet conditions. Surfactant-induced wettability alteration has a great effect on the relative permeabilities of oil and water. The relative permeability of the oil phase increases with the increase of the water-wetness of the solid surface. Seepage laws of oil and water are greatly affected by surfactant-induced wettability alteration. Water flows forward along the pore wall in the water-wet rocks and moves forward along the center of the pores in the oil-wet rocks during the surfactant flooding. For the intermediate-wet system, water uniformly moves forward and the contact angle between the oil–water interface and the pore surface is close to 90°. The direction of capillary force is consistent with the direction of water flooding for the water-wet surface. While for the oil-wet surface, the capillary force direction is opposite to the water-flooding direction. The highest oil recovery by water flooding is obtained at close to neutral wetting conditions and the minimal oil recovery occurs under oil-wet conditions. GRAPHICAL ABSTRACT

Dilational Rheological Properties of P-(n-alkyl)-benzyl Polyoxyethylene Ether Carboxybetaine at Water–Decane Interface

The dilational rheological behaviors of absorbed films of p-(n-alkyl)-benzyl polyoxyethylene ether carboxybetaine CxBE2CB (x = 8, 10, 12) at the water–decane interface have been investigated by the drop-shape analysis method. The influences of time, oscillation frequency, and bulk concentration on dilational modulus and phase angle have been expounded. The experimental results show that the phase angle of CxBE2CB (x = 10, 12) decreases with the increase of time, the slope of the log ϵ − log ω curve and phase angle of CxBE2CB (x = 10, 12) decrease in a wide concentration range. These phenomena become more and more apparent with the increase of hydrocarbon chain length and it cannot be attributed to the diffusion-exchange process between the bulk and the interface. It is reasonable to consider that ethylene oxide groups are flexible and can be compressed and expanded, just like a spring. Therefore, the compression and expansion of the ethylene oxide groups in the interfacial layer and the exchange between interface and sublayer play a more important role for CxBE2CB (x = 10, 12) adsorption film. The dependence of dilational modulus on interfacial pressure can support our provided mechanism strongly.

Interaction between polymer and anionic/nonionic surfactants and its mechanism of enhanced oil recovery

ABSTRACT Various experimental methods were used to investigate interaction between polymer and anionic/nonionic surfactants and mechanisms of enhanced oil recovery by anionic/nonionic surfactants in the present paper. The complex surfactant molecules are adsorbed in the mixed micelles or aggregates formed by the hydrophobic association of hydrophobic groups of polymers, making the surfactant molecules at oil-water interface reduce and the value of interfacial tension between oil and water increase. A dense spatial network structure is formed by the interaction between the mixed aggregates and hydrophobic groups of the polymer molecular chains, making the hydrodynamic volume of the aggregates and the viscosity of the polymer solution increase. Because of the formation of the mixed adsorption layer at oil and water interface by synergistic effect, ultra-low interfacial tension (∼2.0 × 10−3 mN/m) can be achieved between the novel surfactant system and the oil samples in this paper. Because of hydrophobic interaction, wettability alteration of oil-wet surface was induced by the adsorption of the surfactant system on the solid surface. Moreover, the studied surfactant system had a certain degree of spontaneous emulsification ability (D50 = 25.04 µm) and was well emulsified with crude oil after the mechanical oscillation (D50 = 4.27 µm). GRAPHICAL ABSTRACT

Interfacial Dilational Rheology of the Novel Zwitterionic Surfactants

Abstract The dilational rheological properties of series branched betaine surfactants: Guerbet p-(n-tetradecyl)-benzyl carboxybetaine (C14GCB), Guerbet p-(n-dodecyl)-benzyl polyoxyethylene ether(2) carboxybetaine (C12GE2CB), Guerbet p-(n-tetradecyl)-benzyl polyoxyethylene ether(2) carboxybetaine (C14GCB) and Guerbet p-(n-hexadecyl)-benzyl polyoxyethylene ether(2) carboxybetaine (C16GCB), were investigated by drop shape analysis method at the water-decane interface. The dilational properties of surfactants were investigated as a function of time, frequency and concentration. The experimental results show that the time dependence was complex. It was also found that the dilational modulus were almost independent of frequency in the experimental concentration range for C14GE2CB and C16GE2CB, while the dilational modulus of C14GCB and C12GE2CB increased with the increase of frequency, sharing the same results with conventional zwitterionic surfactants. The results indicated the appearance of a more elastic film for the C14GE2CB and C16GE2CB due to the internal compression and expansion of oxyethylene units (EO). On the other hand, the surfactant with branched alkyl chain came forth a higher maximum value of dilational modulus compared with the straight chain surfactants with the increase of concentration, which means the branching of alkyl chain was another important factor to control the interfacial film.

Synthesis and Interfacial Activity of Nonyl Phenol Polyoxyethylene Ether Carboxylate

In order to study the interfacial activity of the anionic-nonionic surfactant, five nonyl phenol polyoxyethylene ether carboxylates were synthesized and mass spectra were used to characterize their structures. The tensions of the anionic–nonionic surfactant aqueous solutions against crude oil were measured and the effects of the surfactant structure, concentration, and salinity on the interfacial activities were discussed. It was shown that nonyl phenol polyoxyethylene (6) ether carboxylate can produce ultralow interfacial tension when the concentrations are not lower than 0.10%, exhibiting a high interfacial activity and a good anti-dilution resistance. Moreover, it was proved that there exists synergism between NaCl and MgCl2 (or CaCl2), which is crucial to achieve the ultralow interfacial tension.