Understanding of the molecular interaction between asphaltenes and other molecules, which may act as its solvents, provides insights into the nature of its stability in petroleum fluids and its phase transitions. Molecular dynamics simulations were performed and reported here on systems consisting of a single asphaltene molecule and pure solvents. Three types of asphaltenes with different architectures, molecular weights, and heteroatoms content were investigated. Water and ortho-xylene were selected to be the interacting solvents. All simulations were performed by using GROMACS software. OPLS_AA potential model for hydrocarbons and SPC/E potential model for water were used in simulations. It was shown that the polar functional groups in asphaltenes were responsible for generating hydrogen bonds (HBs) between asphaltenes and water. It was also demonstrated that both electrostatic (ES) and van der Waals (vdW) interaction energies between asphaltenes and water had important roles. On the contrary, ES between asphaltenes and ortho-xylene had a minor effect as compared with the vdW. In all cases, potential energies increased rather slightly when the pressure was boosted. Moreover, they decreased noticeably when the temperature was raised. HBs between asphaltenes and water were not influenced by pressure change. Additionally, they increased slightly when the temperature was dropped. A Asphaltene COOH carboxyl group D Debye E potential energy ES Electrostatic GROMACS GROningen MAchine for Chemical Simulations Figure 2. Three-dimensional structure snapshot of model asphaltene-water interaction. HBs formed between polar functional groups and water are represented by dashed lines. Color code: water molecules are in red (oxygen) and gray (hydrogen). Model asphaltenes are represented by cyan (carbon), gray (hydrogen), blue (nitrogen), yellow (sulfur), and red (oxygen). In this figure, for clarification purpose, all other water molecules are not shown, except the ones that form HBs with model asphaltenes.Figure 7. RDF of HCOOH -Owater at various temperature and pressure. ConclusionsIn this paper, it is shown that polar functional groups of asphaltenes are responsible for hydrogen bonds generating with water molecules. The total interaction energies between asphaltene and ortho-xylene is much higher than between asphaltene and water. The large size of asphaltene produced strong van der Waals interaction between asphaltenes and solvents. Electrostatic interaction energies between asphaltenes and water were considerable while they were insignificant in the case of asphaltenes and ortho-xylene. The interaction energies decreased perceptibly when temperature was raised while it decreased comparatively when pressure was dropped. . Molecular dynamic simulation of asphaltene co-aggregation with humic acid during oil spill. Chemosphere, 138, 412-421.

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.

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.

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.

In the present study, we report our findings on asphaltenic sludge formation onset during petroleum reservoir acidizing treatment. To achieve this goal, we perform a series of molecular dynamics (MD) simulations at high temperature and pressure (550 K, 200 bar) on asphaltenic-oil (containing different molecular structures of asphaltenes) /hydrochloric acid (HCl) systems. Our simulation results indicate formation of asphaltenic sludge onset due to reservoir acidizing. Accumulation of the ionized asphaltenes at the oil/aqueous interface is the cause of sludge formation onset. Presence of ionized asphaltenes at the oil/water interface is attributed to the strong ion-ion interaction between ionized asphaltenes and acid ions (H+ and Cl-). Sludge formation onset is further stabilized via hydrogen bonding forces between ionized asphaltenes and interfacial water.