Effect of Nanoparticles on Spontaneous Imbibition of Water into Ultraconfined Reservoir Capillary by Molecular Dynamics Simulation

Abstract

Imbibition is one of the key phenomena underlying processes such as oil recovery and others. In this paper, the influence of nanoparticles on spontaneous water imbibition into ultraconfined channels is investigated by molecular dynamics simulation. By combining the dynamic process of imbibition, the water contact angle in the capillary and the relationship of displacement (l) and time (t), a competitive mechanism of nanoparticle effects on spontaneous imbibition is proposed. The results indicate that the addition of nanoparticles decreases the displacement of fluids into the capillary dramatically, and the relationship between displacement and time can be described by l(t) t 1/2. Based on the analysis of the dynamic contact angle and motion behavior of nanoparticles, for water containing hydrophobic nanoparticles, the displacement decreases with the decrease of hydrophobicity, and the properties of fluids, such as viscosity and surface tension, play a major role. While for hydrophilic nanoparticles, the displacement of fluids increases slightly with the increase of hydrophilicity in the water-wet capillary and simulation time, which can be ascribed to disjoining pressure induced by "sticking nanoparticles". This study provides new insights into the complex interactions between nanoparticles and other components in nanofluids in the spontaneous imbibition, which is crucially important to enhanced oil recovery.

Insight into the pressure-induced displacement mechanism for selecting efficient nanofluids in various capillaries

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“…where and were the energy well depth and zero potential distance, represented the To investigate the influence of surface properties of capillary on the displacement, the capillaries were constructed as ideal surfaces, and the characteristic energy (watersw  capillary) was tuned from 0.1 to 0.4 kcal/mol (in 0.05 increment) to form super-hydrophobic, hydrophobic and hydrophilic capillary. 36,37 Here the wettability of capillary was defined based on three-phase contact angle (water-oil-capillary). The value above 150˚ meant superhydrophobic capillary, and between 90˚ and 150˚ showed hydrophobic property, while below 90˚ was hydrophilic capillary.…”

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“…Thus, it is difficult to give an in-depth explanation for the aging process from the microscopic mechanism in the traditional study of insulation aging. However, the molecular structure of materials can be investigated through molecular dynamics simulation, which is helpful to analyze the microscopic mechanisms governing various complex macroscopic phenomena, allowing the connection between microscopic structures and macroscopic properties to be revealed [1,2].…”

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“…The remaining water within the pores can be reasonably considered at bulk conditions, and thus, σ =0.072 N/m and μ =10 −3 Pa ·s at T =300 K. These estimates are performed neglecting the effect of the suspended particles on the imbibition process. However, particle-wall interactions are not negligible at high volume fractions or for particle-pore size ratios close to unit, as local properties of water such as viscosity and contact angle may be altered [55]. Still, the position of the liquid front can be described by Eq.…”