Abstract
It is well accepted that nanofluids have great potential in enhanced oil recovery (EOR). However, the EOR mechanisms by nanofluids largely remain elusive. In the study, the displacement dynamics of residual oil trapped in rough channels by different nanofluids under varied injection pumping forces are investigated by atomistic modeling. Our results indicate that both hydrophilic nanoparticles (NPs) and Janus NPs have highly obvious oil displacement effects. Specifically, hydrophilic NPs increase the viscosity and enlarge the sweeping scope of injected fluid, while Janus NPs favor either staying at the oil–water interface to reduce the interfacial tension or adsorbing onto the convex surface. Under the drag of the injecting flux, Janus NPs displace trapped oil molecules and alter the local surface wettability by sliding along the surface. In contrast, hydrophobic NPs are prone to migrate into the oil phase, which not only reinforces the trapping effect of the oil molecules by the rough surface but also poses a risk of channel blockage. Despite that the oil displacement effect of all the injection fluids is found to be less significant with low pumping force, the Janus NPs are able to maintain a stable oil displacement performance under low pumping force thanks to their sufficiently long contact time with the oil phase. Furthermore, analysis on capillary number indicates that Janus NPs have outstanding application potentials in reservoirs under realistic flooding conditions. Our findings provide atomistic insights into the mechanism of nanofluids in EOR and shed light on the selection and optimization of NPs.
Highlights
Being the most widely used fossil fuel in the world, petroleum is the most important raw material in the modern industrial society [1,2]
This work revealed the displacement mechanisms of trapped oil in the rough channel by injection of nanofluids using Molecular dynamics (MD) simulations
The study indicated that hydrophilic and Janus nano particles (NPs) were able to drive significantly more trapped oil out of rough channels, while hydrophobic NPs had the lowest potential in trapped oil displacement with endan gering probability of channel blockage
Summary
Being the most widely used fossil fuel in the world, petroleum is the most important raw material in the modern industrial society [1,2]. Depending on specific experimental parameters (NPs properties, core properties, flooding rate, residual oil, etc.), different mechanisms may dominate EOR [26]. MD simulation can provide nanoscale dynamics of NPs in oil trapping channels and the underlying mechanisms of nanofluids in EOR, which is challenging to monitor with current experimental capability. The motion pattern and the roles of NPs in EOR in the rough channel are different from the ideally smooth surface adopted in the previous studies. To reveal the realistic displacement dynamics of trapped oil, MD simulations of injecting various nanofluids into rough channels were carried out in this work, aiming to elucidate the EOR mechanisms enabled by different NPs (hydrophilic, hydrophobic, and Janus NPs). The displacement phenomena of trapped oil driven by nanofluids were compared, with the specific role of each NP type in EOR uncovered. The results rationalize the basis of the EOR mechanism by NPs and provide guidance of NPs optimization in pe troleum engineering
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