Tunable stability of oil-containing foam systems with different concentrations of SDS and hydrophobic silica nanoparticles
Graphical abstract
Introduction
Gas flooding [1], [2], [3] is commonly used to improve oil recovery in many oil fields at present, and has become one of the most efficient and popular displacement technologies because of low raw material cost and convenient operation [4], [5]. However, the density and viscosity of the gas are usually too low to drive the crude oil, which will cause viscous fingering in porous medium and have a detrimental effect on oil recovery [6], [7]. The usage of foam fluid is an effective way to improve the apparent viscosity [8], [9], and this has been widely applied in drilling [10], fracturing [11] and enhanced oil recovery (EOR) processes [12].
However, foam is generally unstable both thermodynamically and kinetically [13], [14], especially in the presence of oil. Oil drop can enter the gas–liquid interface of the foam film and separate the gas phase from liquid, thus reducing the foam stability [15]. Adding nanoparticles is one of the most effective methods to enhance the foam stability as it can upgrade the mechanical strength of the foam film. Unlike surfactants, the adsorption of nanoparticles at the gas–liquid interface is normally irreversible [16], [17]. It can also hinder the water flow at bubble surface and thus slow down the thinning process of foam film [13]. Sun et al. [12] compared the residual oil distribution in single SDS and SiO2/SDS foam flooding processes by micromodel flooding. They found that there was more residual oil distribution in single SDS foam flooding process compared with SiO2/SDS foam flooding process, which suggests that the displacement effect of SiO2/SDS foam flooding was better and SiO2 nanoparticles enhanced the foam stability. Similarly, Yekeen et al. [18] investigated the stability of single SDS foam and SiO2/SDS foam in the presence of different kinds of oil by measuring the half-life time. It was found that the half-life of SiO2/SDS foam was longer than that of single SDS foam, which indicates that the SiO2/SDS foam was more stable than single SDS foam. Furthermore, Sun et al. [19] found that the foam stability of SiO2/SDS foam system can be obviously affected by the concentration of SDS and SiO2 nanoparticles. The foam stability reached a maximum level (most of the bubbles remained spherical or ellipsoidal) when the mass fraction of SiO2 nanoparticles and SDS was 1.0% and 0.05%, respectively. Although the effect of various factors on the stability of foam has been intuitively studied by numerous experimental work, the tuning mechanism of foam stability in the foam system containing nanoparticles and oil phase is still not clear.
In this context, we hope to tune the stability of the oil-containing foam system through changing the concentration of constituents (SDS surfactant and SiO2 nanoparticles). Moreover, by employing molecular simulation, a powerful method studying molecular interaction and configuration changes of foam system [20], [21], we study the tuning mechanism at the atomic level. This work is conducive to deepening the understanding of the foam stability tuning mechanism and achieving a more stable foam system in experiment.
Section snippets
Materials
Sodium Dodecyl Sulfate (SDS) with a purity of 92.5%–99.9% was purchased from McLean Biochemical Technology Co., Ltd. SiO2 nanoparticles were purchased from McLean Biochemical Technology Co., Ltd, with a diameter of approximately 30 nm. Dodecyl triethoxysilane with a purity of 97% was purchased from Aladdin Biochemical Technology Co., Ltd. Dodecane with a content of 98.5% was purchased from Wokai biotechnology Co., Ltd. Nitrogen was provided by Shandong Hongda Biological Technology Co., Ltd,
Foam stability and foam morphology
Fig. 4a–c show the change of foam height over time in different systems. Moreover, the half-life time (thalf) was used to characterize the foam stability (Fig. 4d). In this work, thalf was defined as the time when the foam decays to the half of the maximum height, and it was obtained from the foam decay curve. Overall, the foam height increased gradually initially due to the aeration, and then declined after reaching a maximum height. In the foam system with a low SDS concentration (Fig. 4a),
Conclusions
It can be found through experimental study that adding hydrophobic SiO2 in SDS foam system would affect the foam stability to different degrees. With a low SDS concentration (0.2 wt.%), the foam stability was poor, and the stability improvement was very small after adding hydrophobic SiO2 nanoparticles. With a moderate SDS concentration (0.5 wt.%), the foam stability was good, and was first enhanced and then weakened after the addition of hydrophobic SiO2 nanoparticles, and the concentration of
Conflict of interest
The authors declare no competing financial interest.
Acknowledgements
This work was supported by the “National Natural Science Foundation of China” (51874331), the “PetroChina Innovation Foundation” (2018D-5007-0213), the “Shandong Provincial Natural Science Foundation” (ZR2017MEE028), and the “Fundamental Research Funds for the Central Universities” (17CX05023 and 19CX05001A).
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