Molecular dynamics studies of interaction between asphaltenes and solvents

Journal of Petroleum Science and Engineering

2018

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In the present study, we report our findings on various asphaltenes-water interactions at a high reservoir condition (550 K and 200 bar) and the role of water in asphaltene association during the waterflooding process. Molecular dynamics (MD) simulations are performed on oil/water and oil/brine systems. The oil phase is composed of asphaltenes (10 wt%) and o.xylene in which asphaltenes are entirely soluble. Seven different model-asphaltenes with diverse molecular weights, architectures, and heteroatom contents are employed. Interestingly, MD results indicate that asphaltenes become less soluble in oil when water is partially misciblized in the oil phase. All model-asphaltenes containing nitrogen and/or oxygen atoms in their structures are prone to association. The driving force behind asphaltene aggregation is shown to be an asphaltene-water hydrogen bond. The utilization of the brine (3.5 wt% NaCl) instead of pure water induces a slight decrease in asphaltene propensity for aggregation due to salt-in effect. MD results suggest that face-to-face contact is the prominent stacking of asphaltene molecules in their aggregates.All bond lengths are constrained with LINCS algorithm. The long-range electrostatic interactions are computed using a particle mesh Ewald method with a cut-off distance of 1.4 nm. Simulation Results Structural analysis of oil/brine and oil/water systemsThe attracted water molecules reduce the probability of o.xylene near asphaltene monomers and inhibit their ability to solubilize asphaltene molecules. Asphaltene-water interactions minimize asphaltene-asphaltene hydrogen bonds. Employment of brine instead of water enhances the solubility state of model-asphaltenes slightly due to salt-in effect. Face-to-face stacking is the preferred geometry in the asphaltene aggregate. Figure 1. Structures of the seven model-asphaltenes used in this study.Figure 2. Front-view snapshots of simulation results at 550 K and 200 bar. The purpose of these snapshots is to show the mutual miscibility of water (red color) and o.xylene (yellow color) molecules. Also, these snapshots show that asphaltene molecules (black color) and ions (white and blue colors) are settled in oil and brine phases respectively.Figure 3. Configurational snapshots and RDFs of A1, A2, A3, A4, and A7 aggregates. For clarity purpose, the aggregated asphaltene molecules are shown in various colors. All data are computed at 550 K and 200 bar.Figure 4. RDFs of o.xylene (a) and water (b) molecules around the aromatic core of asphaltenes. All data are calculated at 550 K and 200 bar.

Section: Simulation Methodologymentioning

confidence: 99%

Asphaltene aggregation due to waterflooding (A molecular dynamics study)

Journal of Petroleum Science and Engineering

2018

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“…There has been a lack of an understanding of the nature of asphaltenes instability during waterflooding. Recently, we reported a series of special molecular dynamics (MD) studies on the onset of asphaltenes aggregation during a waterflooding process (Yaseen and Mansoori 2017;. Results of our simulation onset are applicable to asphaltenes behavior in real crude oils.…”

Section: Introductionmentioning

confidence: 95%

Microscopic details of asphaltenes aggregation onset during waterflooding

Petroleum Science and Technology

2019

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We report detailed microscopic studies of asphaltenes aggregation onset during waterflooding of petroleum reservoirs. To achieve this objective, a series of simulations are performed on asphaltenic-oil miscibilized with water at high pressure and temperature through molecular dynamics. Results of this simulation onset are applicable to asphaltenes behavior in real crude oils. Our simulation results illustrate that the aggregation onset in waterflooding generally follows three sequential steps: (i) Asphaltene-water interaction; (ii) Water bridging; (iii) Face-to-face stacking. Then, asphaltene-water and water-water hydrogen-bonding network surround every aggregate boosting the intensity of aggregation onset. We intend to utilize such understanding of these details in our predictive and preventive measures of arterial blockage in oil reservoirs during waterflooding.

“…Molecular dynamics (MD) simulation has been applied with much success to investigate the behavior of asphaltenes in various model petroleum fluids (Pacheco-S anchez, Zaragoza, and Mart ınez-Magad an 2004; Takanohashi, Sato, and Tanaka 2004;Hu et al 2011;Yaseen and Mansoori 2017;Khalaf and Mansoori 2018;Mohammed and Mansoori 2018). Recently, we investigated the onset of asphaltene aggregation during waterflooding process.…”

Section: Introductionmentioning

confidence: 99%

Asphaltene aggregation onset during high-salinity waterflooding of reservoirs (a molecular dynamic study)

Petroleum Science and Technology

2018

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The primary objective of this study is to establish an understanding of the role of high-salinity brine on the intensity of asphaltene aggregation onset during waterflooding of petroleum reservoirs. We already have shown that asphaltenes have a high tendency to form aggregates during waterflooding process when pure-and low salinity-water are injected into reservoirs. To fulfill the present objective, molecular dynamic simulations are per-formed on asphaltenic-oil/aqueous systems at 550 K-200 bar. The oil phase consists of asphaltenes (10 wt.%) and ortho-xylene, in which asphaltene molecules are completely soluble. Our simulations results reveal that the "salt-in effect" of high-salinity brine (25 wt.% NaCl) on seven different model asphaltenic oils causes a significant reduction of the onset of asphaltene aggregation as compared with pure-water. Such "salt-in effect" is primarily due to a considerable reduction of water miscibility in the oil phase at high pressure and temperature.