Search

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]