Asphaltene aggregation due to waterflooding (A molecular dynamics study)

Abstract

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.

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

“…It is obvious that asphaltene molecules stay suspended in the oil phase due to the strong van der Waals interaction between asphaltenes and oil (Yaseen and Mansoori 2017). Similarly, salt-ions do not diffuse into the oil phase due to the strong interactions between water and ions (Yaseen and Mansoori 2018). On the other hand, the schematic representation shows that oil and water present mutual miscibility.…”

“…RDFs of the center of mass of asphaltene moieties are calculated (see Figure 4). The heights of RDF peaks are used to compare the intensity of asphaltene aggregation of various simulations ( Mohammed and Mansoori 2018;Yaseen and Mansoori 2018). PW exhibit the highest RDF peaks, which indicate that pure-water causes the highest intensity of asphaltene aggregation.…”

Spotlight onto surfactant–steam–bitumen interfacial behavior via molecular dynamics simulation

“…Then geometry optimization was applied to the simulation box, and an Isothermal–isobaric (NPT) ensemble at 5 MPa and 498 K followed to gain a reasonable density at a typical oil sands reservoir pressure under a steam-assisted gravity drainage (SAGD) process. Figure S1 illustrates the molecular structures of the asphaltene, saturate, resin, aromatic, and anionic surfactant molecules used in this study 50 , 55 , 58 , 98 , 99 . To create a surfactant solution, 4000 water molecules and four surfactant molecules were placed into a 6 × 6 × 12 nm simulation box.…”

A Numerical Approach to Investigate the Impact of Acid-Asphaltene Sludge Formation on Wormholing During Carbonate Acidizing

“…Therefore, chemical reaction is the determining mechanism of asphaltene deposition. A number of researchers developed different models and investigated asphaltene [58][59][60][61][62]. However, it was found that the deposition of asphaltene is controlled by chemical interactions of injected fluid and oil.…”