Abstract
The ultra-low permeability reservoir is regarded as an important energy source for oil and gas resource development and is attracting more and more attention. In this work, the active silica nanofluids were prepared by modified active silica nanoparticles and surfactant BSSB-12. The dispersion stability tests showed that the hydraulic radius of nanofluids was 58.59 nm and the zeta potential was − 48.39 mV. The active nanofluids can simultaneously regulate liquid–liquid interface and solid–liquid interface. The nanofluids can reduce the oil/water interfacial tension (IFT) from 23.5 to 6.7 mN/m, and the oil/water/solid contact angle was altered from 42° to 145°. The spontaneous imbibition tests showed that the oil recovery of 0.1 wt% active nanofluids was 20.5% and 8.5% higher than that of 3 wt% NaCl solution and 0.1 wt% BSSB-12 solution. Finally, the effects of nanofluids on dynamic contact angle, dynamic interfacial tension and moduli were studied from the adsorption behavior of nanofluids at solid–liquid and liquid–liquid interface. The oil detaching and transporting are completed by synergistic effect of wettability alteration and interfacial tension reduction. The findings of this study can help in better understanding of active nanofluids for EOR in ultra-low permeability reservoirs.
Highlights
With the technology development of oil and gas exploration, unconventional oil and gas resources have become a new global energy supply
Xie et al (2005) pointed out that spontaneous imbibition recovery rate was faster in nonionic surfactant solutions than in cationic surfactant solutions owing to the lower interfacial tension
According to the evaluation experiment of oil dischargement during spontaneous imbibition, the oil recovery of active nanofluids is higher than that of pure surfactant solution and brine, which can be ascribed to the synergistic effect of active silica nanoparticles and BSSB-12
Summary
With the technology development of oil and gas exploration, unconventional oil and gas resources have become a new global energy supply. Surfactants are commonly used as spontaneous imbibition agents, which can enhance oil recovery primarily through reducing interfacial tension (IFT) and altering wettability. Li et al (Li et al 2017a) presented that the silica-based nanofluid is a promising method to enhance oil recovery in water-wet sandstone reservoirs by altering the wettability to neutral-wet. When combining nanoparticles and surfactants together, the interfacial tension can be reduced and wettability can be altered This type of nanofluids ( called active nanofluids) has higher oil displacement potential than pure surfactant solutions or pure nanofluids. The nanofluids can simultaneously regulate oil/water and oil/solid interface to reduce interfacial tension and alter wettability. It can improve the oil displacement in ultra-low permeability reservoirs through synergistic effect of surfactant and nanosilica. The active silica nanofluids are not suitable for reservoir brine with high divalent ion contents, such as Ca2+ and Mg2+
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