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To explore the influence of different wax components and the shear effect exerted by the pump and pipe wall in the process of crude oil pipeline transportation on the microbehavior of wax aggregation in crude oil at low temperatures, molecular dynamics models of binary and multivariate systems of crude oil with different wax components are established in this paper. The simulation results are compared with the existing experimental results and the NIST database to verify the rationality and accuracy of the models. By using the established binary model to simulate four crude oil systems containing different wax components, it can be found that the longer the wax molecular chain, the more easily the wax molecules aggregate. The influence of temperature on the aggregation process of wax molecules with different chain lengths is also studied. The lower the temperature, the greater the difference in wax molecular aggregation degree caused by the difference in molecular chain length. Nonequilibrium molecular dynamics is used to simulate the shear process of a multivariate system of crude oil, and the micromechanisms of the shear effect on the aggregation process of wax molecules are studied. Shearing can destroy the stable structure of crude oil, resulting in the orientation and conformational transformation of wax molecules, and obtaining the region of wax molecules sensitive to temperature and shear effects, the temperatures of which are below the wax precipitation point and the shear rate of which is lower than the maximum shear rate to prevent the molecular structure from being destroyed. At the same time, the sensitivity of wax components with different chain lengths to the shear effect is studied. The research results provide theoretical guidance for ensuring the safe and economic operation of waxy crude oil production. [ABSTRACT FROM AUTHOR]

To ensure the safe and economic operation of a waxy crude oil production process, the microdynamic mechanism and thermodynamic characteristics of the wax gelation process need to be revealed at nanoscale. The molecular dynamics model was established to characterize the phase transition and gelation behavior of waxy molecules in a multiphase system (including oil, asphaltene and water). The relative error between the simulated results and experimental data measured by Dutour et al. (2002) was less than 5%. Under the coupling effect of different operation parameters, the molecular dynamics simulation was employed. The simulated results showed that the spherical paraffin crystals underwent the processes of dissolution, diffusion and aggregation. After which waxy cluster crystals with larger amount but smaller volume were formed, which would be deposited on the inner wall under the concentration gradient. The influence mechanisms of different operating parameters on wax gelation were analyzed. And it was found that the increase in temperature and water cut decrease the wax precipitation, while the increase in pressure enhance the wax precipitation rate. Furthermore, by means of hydrogen bonding and the effect of similar dissolution, water and asphaltene molecules also affect the wax precipitation process at the molecular scale. The investigations in this study provide theoretical support for the paraffin removal and control in a waxy crude oil production system. The molecular dynamics model and details. Image 1 • The MD model for characterizing the phase transition and gelation behavior of waxy molecules is established. • The microscopic mechanism of dissolution, diffusion and aggregation process of waxy crystals is revealed. • The influence mechanism of different operation parameters on phase transition and gelation process is studied. • We have confirmed that the hydrogen bond with the structure of C − H ⋯ O will form between water and waxy molecules. [ABSTRACT FROM AUTHOR]

Based on the background of oilfield chemical flooding produced liquid treatment projects, to achieve new insight into the micromechanism of the impact of polymer molecules applied to enhanced oil recovery (EOR) technology on the crude oil−water interface behavior, different "crude oil/HPAM/produced water" interface simulation systems were constructed by regulating the polymerization degree and hydrolysis degree of partially hydrolyzed polyacrylamide (HPAM) and combining the composition and physical properties of oil and water phases. The simulated results showed that all simulation systems have a stable layer order and clear crude oil−water interface after dynamic relaxation equilibrium. HPAM molecules were agglomerated in different forms at the crude oil−water interface depending on the inorganic cations in the water phase and their own degree of polymerization and hydrolysis, and the order of inorganic cations aggravating the agglomeration was Ca2+>Na+>K+>Mg2+. The stability of the interfacial film was positively correlated with the gyration radius of the HPAM molecules. Unlike the continuous increase in the gyration radius of HPAM molecules with increasing polymerization degree, the effect of increasing hydrolysis degree on the stability of the crude oil−water interfacial film is concentrated in the range of 15–35%, the gyration radius of HPAM molecules no longer increases when the hydrolysis degree continues to increase, and the interfacial film stability no longer significantly changes. [Display omitted] • A multicomponent molecular dynamics crude oil−water interfacial simulation system is established according to the experimental results. • Oil−water interfacial behavior of "blanket" shaped agglomerated HPAM molecules. • The micromechanism of inorganic ions accelerating HPAM agglomeration and the order of impact ability were revealed. • Available approach for characterizing HPAM polymerization degree and hydrolysis degree on the stability of crude oil−water interfacial film. [ABSTRACT FROM AUTHOR]