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Extended surfactants have shown great potential in enhanced oil recovery (EOR). In this paper, the effects of extended surfactant concentration, polypropylene oxide (PO) number, and various counter ions (Na+, Ca2+, and Mg2+) on the oil-water interfacial tension (IFT) of extended surfactant solutions were investigated in detail. The selected extended surfactants were sodium dodecyl polyoxypropylene sulfate (L-C12POmS, m=5, 10, 15). Based on our experimental results, under NaCl conditions, with an increase in the PO number, the space occupied by the surfactant molecules on the side of the oil phase increases, which matches the size of the anionic head, and the surfactant film becomes tight. An ultralow IFT value appears for L-C12PO15S at 0.5% NaCl against decane. The addition of bivalent cations can significantly reduce the IFT. As the Ca2+ concentration increases, IFTs of APS solutions against alkanes can achieve ultralow values at lower PO numbers and against alkanes with a wide ACN range. For the MgCl2 system, the smaller hydration radius of Mg2+ improves the tightness of the anionic head, resulting in a crowded arrangement of the PO chains on the oil phase side. Therefore, the ability of Mg2+ to reduce the IFT against alkanes is weaker than that of Ca2+. Moreover, the surface-active substances in the crude oil adsorb competitively on the interface, resulting in an increase in IFT. By adding Ca2+or Mg2+, a tight adsorption film of surfactant molecules will be formed, and the IFT value reaches ultralow against crude oil. The studies in this paper have important implications for the application of extended surfactant solutions to enhance oil recovery under high salt reservoir conditions.

Open-cell foams consisting of interconnected struts are widely used in thermal applications such as volumetric solar receivers. The thermal performance of foams strongly relies on their radiative behaviors which intrinsically depends on the radiative properties of struts. This study proposed a feasible approach to determine the radiative properties of solid struts by a pore scale identification from a macro scale measurement. First, the normal-hemispherical transmittance and reflectance spectra of two nickel foams were measured by an experimental system. Second, a pore scale forward calculation was conducted by a combination of Monte Carlo Ray-tracing method and real foam structures obtained from micro-computed tomography technique. Last, an Adaptive Particle Swarm Optimization algorithm was adopted to retrieve the spectral reflectivity and specularity of nickel struts from the measured spectra. The results show that it is unreasonable to assume the reflection behavior of strut surface simply as either specular or diffused, and also, it is unreliable to assign the reflectivity of strut surface directly by Fresnel's law. Within the investigated wavebands 0.4–2.2 μm, the average reflectivity of nickel struts is 12% lower than that of a nickel mirror. The proportion of specular reflection at nickel strut surface is between 37%–52%, almost increasing with wavelengths.

Betaines and anionic-nonionic surfactants are suitable for applying in enhanced oil recovery (EOR) in the high-temperature and high-salinity reservoir conditions. We have used the spinning drop method to investigate the interfacial tension (IFT) values of alkyl carboxylicbetaine (ACB) and five types of anionic-nonionic surfactant (C14E3C, C16E3C, C18E3C, C18E5C and C18E10C) with different ethylene oxide (EO) numbers and different alkyl chain lengths against hydrocarbons and crude oil. Thereafter, under the same conditions, the IFT values of ACB and anionic-nonionic surfactant mixed solutions have also been investigated. The experimental results exhibit that for achieving ultralow IFT the proper hydrophilic-lipophilic balance (HLB) is prerequisite, but the tightness of the adsorption film is the key factor, which is controlled by the consistency of the spaces occupied at the oil side and the water side of an interface. This mechanism is so called “size compatibility”. The ultralow level IFTs have been reached during wider concentration ranges as the mixed systems against crude oil, which have not happened when the hydrocarbons are the oil phase. These phenomena demonstrate the strong synergistic effect among ACB, anionic-nonionic surfactant and natural surface-active materials, which is important for the development of high-temperature and high-salinity oil reservoirs.

High-temperature radiative properties of open-cell foams are relatively scarce due to measurement limitation. This study aims to numerically predict the volumetric radiative properties of irregular open-cell foams at high temperatures. The prediction is based on established relations which link the volumetric radiative properties to the structural parameters and/or component optical/radiative properties. Four typical foams are considered, including copper foams, nickel foams, zirconia foams and alumina foams. Former two are made of opaque metals, while latter two are made of semitransparent oxidized ceramics. For the four foams, the highest temperatures investigated are up to 1084 K, 1605 K, 1633 K and 2300 K, respectively. The variations of radiative properties with wavelength and temperature are analyzed. It was found that high temperature can strengthen radiation absorption inside metal and ceramic foams at most of wavebands. The temperature has almost no influence on the scattering phase function of metal and ceramic foams. Compared to copper foams, the nickel foams behave more absorbing at most of wavebands and temperatures. Alumina foams show an obviously forward predominance (asymmetry factor g > 0.4), and the fraction of forward scattering increases with increasing wavelength. Zirconia foams show a slight backward predominance (asymmetry factor g = -0.1) at short wavelengths, and a closely isotropic scattering was found at around wavelength λ = 7 μm. This study provides a feasible way to obtain the radiative properties of open-cell foams at high temperatures. Normal-normal transmittance and normal-hemispherical transmittance/reflectance of foams were measured at room temperature. The experimental results validate the numerical approach to obtaining radiative properties from analytical relations and bulk properties.