Molecular dynamics simulation of magnetic field influence on waxy crude oil

Microscopic Mechanism for Gradient Diffusion of Salt-Containing Droplets Induced by Electromagnetic Synergy: A Molecular Dynamics Study

The electromagnetic synergy has been proven to be highly effective in separating oil-water emulsions. However, the dynamic impact mechanism of electromagnetic fields on the internal structure of salt droplets remains unclear. In this study, the molecular dynamics (MD) simulation was used to investigate the molecular diffusion of salt ions and water molecules, as well as the dynamic behavior of droplets under the combined influence of electromagnetic fields. The results indicate that ions accumulate in the electromagnetic synergistic field, causing the deformation amplitude of droplets to be smaller than that in a single electric field. The magnetic field affects the energy of the system, when the magnetic field strength is between 1 and 5T, the nonbonded energy significantly increases nonlinearly; when the magnetic field strength is greater than 5T, the total energy of the system significantly changes. In addition, the viscosity of the medium is significantly lower when the intensity of the magnetic and electric fields is controlled within a specific range, providing a new way to regulate the fluidity of fluids.

Experimental study of the effects of a magnetic field/magnetic field-ferromagnetic nanocomposite pour point depressant on wax deposition

A magnetic field and pour point depressant, as a new avenue for improving the submarine pipeline flow of waxy oils, has attracted increasing attention along with the development of efficient wax mitigation techniques. Although advances have been made recently in understanding the rheological behavior and crystallization properties of waxy oils, the effect of magnetic field and pour point depressants on wax deposition remains an open question. In this work, a ferromagnetic nanocomposite pour point depressant (FNPPD) was prepared. The variations in wax deposition mass and component under the effect of different magnetic treatments and magnetic field-FNPPDs were investigated using cold fingers and high-temperature gas chromatography. It was evident that both the high-intensity and high-frequency magnetic fields generated by the magnet and magnetic coil can effectively reduce the deposition mass and have a long-term magnetic history effect. The synergistic effect of magnetic fields and FNPPDs concurrently reduced the thickness/mass and wax content in the deposition layer, as compared to the individual use of magnetic fields or FNPPDs. The wax precipitation properties and wax crystal morphology of waxy oils under the action of the magnetic field were characterized by differential scanning calorimetry, focused beam reflectance measurement and polarizing microscopy experiments, and the mechanism of the magnetic field was elaborated from the perspective of crystallization kinetics by combining the fitting analysis of Avrami and size-independent growth model.

Molecular Dynamics Simulation of the Synergistic Effect of Alkali/Surfactant/Polymer on the Formation and Stabilization of Water-Based Foam Systems

The stable maintenance effect of a chemical oil displacement agent on a foam liquid film usually creates problems with the oilfields surface system. To achieve comprehensive insights into the influence mechanism of these chemical agent components on the foam liquid film, an "SDBS/HPAM/OH^-" water-based foam simulation system and corresponding control systems were constructed by adjusting the categories and quantities of component molecules by molecular dynamics (MD) simulation. The simulated results indicated that the foam stability follows the order of "SDBS/HPAM/OH^-" system > "SDBS/HPAM" system > "SDBS" system. The smaller the inclination angle of the SDBS molecular tail chain, the greater the tendency of the SDBS molecular configuration to be "upright" at the gas-liquid interface, which is not conducive to preventing the aggregation and penetration of gas molecules at the gas-liquid interface. Although the presence of HPAM molecules can significantly enhance the stability of the liquid film by restricting the liquid film's drainage and the diffusion of gas molecules, the addition of HPAM molecules would weaken the formation ability of the foam liquid film. Through decreasing the aggregation of cations around the co-adsorption layer, OH^- not only enhances the interfacial activity of SDBS molecules, but also reduces the electrostatic repulsion between -COO^- groups on the HPAM molecular chain, which makes the foam more stable. With an increase in the pH, SDBS concentration, and HPAM concentration, the stability of foam liquid film was strengthened. These results are helpful in facilitating new insights into the formation and stabilization mechanism of water-based foams. In particular, they provide support for the development and application of new defoaming technologies.

Effect of Wax Composition and Shear Force on Wax Aggregation Behavior in Crude Oil: A Molecular Dynamics Simulation Study

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.

Molecular Dynamics Simulation and Experiment on the Microscopic Mechanism of the Effect of Wax Crystals on the Burst and Drainage of Foams

In recent years, with the goal of “carbon peaking and carbon neutralization”, the CO2 flooding technology in carbon capture, utilization, and storage (CCUs) has been paid great attention to the oil fields. However, the CO2 flooding of crude oil may produce foams in the oil and gas separation process. In addition, the precipitation of wax components in crude oil might enhance the stability characteristics of these foams and lower the separator’s efficiency. Based on a crude oil depressurization foaming device, the influence of wax crystals on the bursting of oil foam was studied using simulated oil, and the microstructure of the wax crystal and foam liquid film was observed using freeze-etching and microscopic observation. In addition, the gas–liquid interface model of the wax oil was established by a molecular dynamics (MD) simulation to analyze the influence mechanism of wax crystals on foam drainage and gas diffusion among foams in the microlayer. The results show that the precipitation of wax crystals overall reduces the rate of defoaming and drainage and increases the grain diameter of the foam. The formation and growth of the wax crystal-shaped network impede the flow of liquid in the drainage channel and stabilize the foam. Moreover, it impedes the diffusion of CO2 among foams, inhibiting the bursting of the foams. The results of the combined experiments and MD simulation verify the accuracy and applicability of the molecular model, which further clarifies the effect of wax crystals on foam stability and its mechanism of action on foam film. These findings are a benchmark for the enhancement of defoaming and separation efficiency and a theoretical framework for future study and modeling.

Electromagnetic bioeffects: a multiscale molecular simulation perspective

Electromagnetic bioeffects remain an enigma from both the experimental and theoretical perspectives despite the ubiquitous presence of related technologies in contemporary life. Multiscale computational modelling can provide valuable insights into biochemical systems and predict how they will be perturbed by external stimuli. At a microscopic level, it can be used to determine what (sub)molecular scale reactions various stimuli might induce; at a macroscopic level, it can be used to examine how these changes affect dynamic behaviour of essential molecules within the crowded biomolecular milieu in living tissues. In this review, we summarise and evaluate recent computational studies that examined the impact of externally applied electric and electromagnetic fields on biologically relevant molecular systems. First, we briefly outline the various methodological approaches that have been employed to study static and oscillating field effects across different time and length scales. The practical value of such modelling is then illustrated through representative case-studies that showcase the diverse effects of electric and electromagnetic field on the main physiological solvent - water, and the essential biomolecules - DNA, proteins, lipids, as well as some novel biomedically relevant nanomaterials. The implications and relevance of the theoretical multiscale modelling to practical applications in therapeutic medicine are also discussed. Finally, we summarise ongoing challenges and potential opportunities for theoretical modelling to advance the current understanding of electromagnetic bioeffects for their modulation and/or beneficial exploitation in biomedicine and industry.

Transport Properties of Waxy Crude Oil: A Molecular Dynamics Simulation Study

To study the effects of paraffin on viscosity of waxy crude oil and transport properties of small molecules, light and waxy crude oil models were investigated at atmospheric pressure and 293-323 K temperature range using atomistic molecular dynamics simulations. The optimized parameters for liquid simulations all-atom (OPLS-AA) and atomistic polarizable potential for liquids, electrolytes, and polymers (APPLE&P) force fields were employed. The self-diffusion coefficients, viscosity, and paraffin configurations were compared for two oil models and between the two employed force fields. However, the behavior of paraffin molecules predicted by two force fields was quite different. Simulations using the OPLS-AA force field showed crystallization of longer paraffin molecules below 323 K, while simulations with the APPLE&P force field demonstrated a homogeneous mixture down to 293 K. To provide additional validation of the employed force fields, the density, diffusion coefficient, and crystallization of pure alkanes were compared with experimental data. The density and diffusion coefficients of n-C₆ and n-C₁₄ simulated with the APPLE&P force field were found to be in much closer agreement with the experimental data. The OPLS-AA force field was found to overestimate the crystallization temperature of pure alkanes. Therefore, simulations with the APPLE&P provide more realistic description of the waxy oil structure and transport properties. In this temperature range, the paraffin molecules are homogeneously distributed in the mixture, and viscosity of the system increased by a factor of two compared to light oil. Crystallization of paraffins requires lower temperatures or/and the presence of other components such as nanoparticles or asphaltene molecules to facilitate nucleation.

Implementation of magnetic field force in molecular dynamics algorithm: NAMD source code version 2.12

The external fields, such as the magnetic force, have made advances in many industrial and biotechnology applications during the past century, although the changes in the structure of materials under the impact of the electromagnetic fields have not entirely been clear yet. The molecular simulation technique by providing extensive data from the configuration and orientations of the atoms is becoming the effective useful tool for scientists in a wide range of research areas. This paper presents an extended velocity Verlet algorithm inside the Nanoscale Molecular Dynamics (NAMD) package that enhances the NAMD features with the capability to compute the magnetic field force. We described how this novel feature has been implemented inside the package. Moreover, the results are reported for the rotation of a charged particle, and the thermo-physical properties of water in the presence of a magnetic field confirming how this developed NAMD source code provides accurate measurements compared with other available data.