Janus nanoparticles (JNPs) exhibit significant promise for enhancing oil recovery (EOR). However, their large-scale field deployment remains challenging. A key challenge lies in the insufficient understanding of how the physical characteristics of JNPs influence their transport behavior and microscopic oil displacement mechanisms in porous media. In this study, molecular dynamics (MD) simulations are employed to systematically investigate the displacement dynamics of oil trapped on rough surfaces mediated by JNPs of various geometries. The results reveal that particle shape critically affects both the pinning resistance encountered at groove edges and the accumulation patterns along lateral walls. These shape-dependent adsorption configurations in turn modulate local wettability and ultimately dictate the efficiency of oil removal from nanoscale grooves. Spherical and ellipsoidal JNPs demonstrate superior displacement performance when the groove surface is coated with a thin oil film. However, under conditions involving thick oil films, spherical JNPs exhibit limited penetration into narrow grooves due to their stable orientation at the oil–water interface, which reflects strong interfacial stability. In contrast, disc, rod, and ellipsoidal JNPs effectively disrupt thick oil films via a cooperative mechanism termed “aggregation and flipping”. Among all evaluated geometries, ellipsoidal JNPs consistently deliver optimal EOR performance across various oil film conditions. These findings provide molecular-level insights into shape-governed JNP performance in EOR, offering valuable guidance for the rational design and application of shape-optimized JNPs in oilfield operations.

The rapid secondary formation of gas hydrate is a potential cause of flowline blockage in deepwater oil and gas production systems, posing serious flow assurance challenges. However, its microscopic formation mechanism remains an area of active research. Recently, the residual structure hypothesis has gained significant attention in explaining the rapid secondary formation of hydrates. In this study, massive molecular dynamics simulations are conducted to investigate the secondary formation of methane hydrates in solutions containing hydrate residual structures of varying sizes. The results indicated that residual structures, owing to their hydrate-like characteristics, facilitate the adsorption and capture of methane molecules, leading to the formation of local gas supersaturation regions. Residual structures promote hydrate formation through two key mechanisms: acting as nucleation sites and supplementing methane concentrations. Particularly, a synergy between residual structures and gas concentration was identified: high gas concentrations stabilize small residual structures, allowing them to serve as nucleation sites, while large stable structures can enrich methane even under low gas concentration.

This work not only provided a detailed understanding of the mechanisms of hydrate secondary formation but also provided valuable insight for hydrate blockage prediction and control in subsea oil and gas pipelines, contributing to improved flow assurance strategies.

Janus nanoparticles (JNPs) possess great potential in recovering the residual oil from reservoirs, however, the fundamental interaction mechanisms among nanoparticles, the oil, and reservoir wall characteristics remain to be elucidated. In this work, models of oil trapping grooves with different geometric features are subjected to molecular dynamics simulations for investigating the influences of roughness parameters on oil displacement dynamics by JNPs. Four key surface geometry parameters and different degrees of surface hydrophobicity are considered. Our results indicate that JNPs hold an outstanding performance in displacing residual oil on weakly to moderately hydrophobic surfaces. Overall, smaller entry and exit angles, the larger aspect ratio of the oil trapping grooves, and a bigger tip length of the rough ridges lead to superior oil recovery. Among the key geometric parameters, the aspect ratio of the oil trapping grooves plays the dominant role. These insights about the interaction of surface properties and JNPs and the resulting trapped oil displacement could serve as a theoretical reference for the application of JNPs for targeted reservoir conditions.