Molecular Dynamics Simulation of the Nucleation and Gelation Process for a Waxy Crude Oil Multiphase System under Different Physical–Chemical Influencing Factors

Gan, Yifan; Cheng, Qinglin; Wang, Zhihua; Yang, Jian; Liu, Yang

doi:10.1021/acs.energyfuels.9b02019

Cited by 19 publications

(12 citation statements)

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“…The above indicated that the clusters aggregation occurred in these positions, and from outside to inside, the element composition of cluster was water, oil, asphaltene, and wax. Furthermore, through comparing the RDF values of nucleated cluster of Figure a at 2000 ps in ref (this nucleated cluster was also the initial model adopted in this paper) to the results in this paper of 1000 ps, it could be concluded that the element composition of each layer was basically the same as that of the initial nucleated cluster. But the peak value of each molecule at 1000 ps was lower, which indicated that some molecules around the cluster began to move away from the nucleation center and gradually accumulated on the pipeline wall.…”

Section: Resultsmentioning

confidence: 66%

“…Step 2: For the system model of the nucleated clusters. In this paper, we directly adopted the 2000 ps MD simulation results of the heterogeneous (rectangular nucleation center) nucleation process which had been simulated by our research group in ref . In this way, the complete deposition and wall sticking process of nucleated clusters on the pipeline wall could be simulated.…”

Section: Simulation Methodologymentioning

confidence: 99%

“…In previous studies, , our research group had explored the micro mechanism of the phase transition and wax precipitation behavior and the nucleation and gelation behavior for wax crude oil multiphase system pipeline transportation (shown in Figure ). The research had found that the solid waxy crystals would first dissolve in the multiphase system, and then they would diffuse and form the irregular distribution.…”

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Simulation of Waxy Crude Oil Multiphase System Depositing and Sticking on Pipeline Inner Walls and the Micro Influence Mechanism of Surface Physical–Chemical Characteristics

et al. 2021

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For ensuring the safe and stable operation of waxy crude oil pipeline transportation, in this research, the molecular dynamics model was established to characterize the deposition and wall sticking behavior of waxy crude oil multiphase system pipeline transportation. The equal density interpolation fitting method was proposed to determine the wall contact angle of simulation results. Through verification, the error between the simulation results and the experimental results measured by Dos Santos et al. (2006) was less than 5%, which showed that the established model was accurate and reliable. Using the established model, the deposition and wall sticking behavior of waxy crude oil nucleated clusters was simulated. It was found that the nucleated clusters would first adhere to the wall surface to form the solidified oil layer. Then, the wax and asphaltene molecules would diffuse to the deposit layer, and the oil molecules in the solidified oil layer reverse diffused to the direction of the oil flow. With the adhering and spreading degree of clusters on the wall surface increasing, the deposit layer gradually aged, and the gelled deposit layer with a higher density and hardness would form. On this basis, the micro influence mechanism of the surface free energy was studied. It was found that the higher the surface free energy, the more hydrophilic the pipeline wall was, and the higher the adhesion degree would be. Moreover, based on the ABF sampling and the potential of mean force calculations, the selective deposition process of waxy crude oil deposited on the sedimentary layer was studied. The micro information on the deposition sites, the binding conformation, and the binding energy of different molecules in clusters deposited on different molecules in sedimentary layer were analyzed. The investigations in this study could provide theoretical support for paraffin removal and control, which could ensure the safe and stable operation of the waxy crude oil production system.

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Section: Resultsmentioning

confidence: 66%

Section: Simulation Methodologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Simulation of Waxy Crude Oil Multiphase System Depositing and Sticking on Pipeline Inner Walls and the Micro Influence Mechanism of Surface Physical–Chemical Characteristics

et al. 2021

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“…The bond interaction potential includes the bond expansion potential energy, bond angle bending potential energy and dihedral angle distortion potential energy. The nonbond interaction consists of van der Waals interaction potential energy and electrostatic interaction potential energy [ 25 , 26 ]. The potential function used for each force is shown in Figure 2 .…”

Section: Models and Simulationmentioning

confidence: 99%

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

Wang

Cheng

Gan³

et al. 2022

Molecules

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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.

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“…Finally, for the optimized model, it was subjected to a 1000 ps dynamics simulation in the NVT ensemble with temperatures of 318.15, 308.15, 298.15, 288.15, and 278.15 K. The convergence criterion was that the temperature and energy profile of the model fluctuated within 5%, and then, the model was simulated in the NVE ensemble for 400 ps to use the calculated results. The potential functions of all atoms and the parameters of the interatomic interactions in the model were assigned by the COMPASS force field. ,, The initial velocity of each molecule in the starting state was given randomly according to the Boltzmann distribution, and periodic boundary conditions were used in each direction of the model. The inter-particle van der Waals interactions were determined using an atom-based algorithm with a truncation radius of 15.5 Å.…”

Section: Simulationmentioning

confidence: 99%

Effect of a Coated Wall on Wax–Asphaltene Molecule Diffusion, Aggregation, and Adhesion Mechanism: A Molecular Dynamics Simulation Study

Wang

Liu

et al. 2022

Energy Fuels

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Coating is increasingly used as a cost-effective strategy for controlling heavy component deposition in waxy crude oil transportation flowlines. This paper systematically investigated the micro influence mechanism of the coated wall on the diffusion, aggregation, and adhesion behavior of wax–asphaltene molecules by the molecular dynamics (MD) method. A set of experiments was performed to determine the properties of the waxy crude oil. For overcoming the limitations of the model simplification of previous MD studies, the MD models based on experimental data were developed to characterize the motion behavior of wax–asphaltene molecules on non-coated and coated wall surfaces, and the simulated densities of crude oil components had an error of less than 5% with the National Institute of Standards and Technology (NIST) data, which showed that the established model was accurate and reliable. The simulation results showed that two condensate oil layers were formed on the non-coated wall surface, the diffusion and aggregation behavior of wax–asphaltene molecules were enhanced under the low-temperature condition, and there was considerably heavy component molecules adhesion to the non-coated wall surface. The analysis of mean square displacement, radial distribution function, and relative concentration distribution revealed that 288.15 K was the peak wax precipitation, which was consistent with the experimental conclusion. It was also found that the presence of low surface energy coating weakened the diffusion of heavy component molecules. The epoxy silicone-coated had the weakest interaction with wax–asphaltene molecules. Moreover, the fact that the coated wall had a certain inhibitory effect on the aggregation and adhesion of wax–asphaltene molecules in the pipeline was proven, where the epoxy silicone-coated had the strongest inhibitory effect. These investigations present new insights and guidance for controlling heavy component deposition by coating in the pipeline transportation process of waxy crude oil.

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Molecular Dynamics Simulation of the Nucleation and Gelation Process for a Waxy Crude Oil Multiphase System under Different Physical–Chemical Influencing Factors

Cited by 19 publications

References 58 publications

Molecular Dynamics Simulation of Waxy Crude Oil Multiphase System Depositing and Sticking on Pipeline Inner Walls and the Micro Influence Mechanism of Surface Physical–Chemical Characteristics

Molecular Dynamics Simulation of Waxy Crude Oil Multiphase System Depositing and Sticking on Pipeline Inner Walls and the Micro Influence Mechanism of Surface Physical–Chemical Characteristics

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

Effect of a Coated Wall on Wax–Asphaltene Molecule Diffusion, Aggregation, and Adhesion Mechanism: A Molecular Dynamics Simulation Study

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