TY - JOUR
T1 - Multi-scale simulation of asphaltene aggregation and deposition in capillary flow
AU - Boek, Edo S.
AU - Headen, Thomas F.
AU - Padding, Johan T.
PY - 2009
Y1 - 2009
N2 - Asphaltenes are known as the 'cholesterol' of crude oil. They form nano-aggregates, precipitate, adhere to surfaces, block rock pores and may alter the wetting characteristics of mineral surfaces within the reservoir, hindering oil recovery efficiency. Despite a significant research effort, the structure, aggregation and deposition of asphaltenes under flowing conditions remain poorly understood. For this reason, we have investigated asphaltenes, their aggregation and their deposition in capillary flow using multi-scale simulations and experiments. At the colloid scale, we use a hybrid simulation approach: for the solvent, we used the stochastic rotation dynamics (also known as multi particle collision dynamics) simulation method, which provides both hydrodynamics and Brownian motion. This is coupled to a coarse-grained MD approach for the asphaltene colloids. The colloids interact through a screened Coulomb potential with varying well depth ε. We tune the flow rate to obtain Peflow ≫ 1 (hydrodynamic interactions dominate) and Re ≪ 1 (Stokes flow). Imposing a constant pressure drop over the capillary length, we observe that the transient solvent flow rate decreases with increasing well depth ε. The interactions between the mesoscopic asphaltene colloids can be related to atomistic MD simulations. Molecular structures for the atomistic calculations were obtained using the quantitative molecular representation approach. Using these structures, we calculate the potential of mean force (PMF) between pairs of asphaltene molecules in an explicit solvent. We obtain a reasonable fit using a -1/r2 attraction for the attractive tail of the PMF at intermediate distances. We speculate that this is due to the two-dimensional nature of the asphaltene molecules. Finally, we discuss how we can relate this interaction to the mesoscopic colloid aggregate interaction. We assume that the colloidal aggregates consist of nano-aggregates. Taking into account observed solvent entrainment effects, we deduct the presence of lubrication layers between the nano-aggregates, which leads to a significant screening of the direct asphaltene-asphaltene interactions.
AB - Asphaltenes are known as the 'cholesterol' of crude oil. They form nano-aggregates, precipitate, adhere to surfaces, block rock pores and may alter the wetting characteristics of mineral surfaces within the reservoir, hindering oil recovery efficiency. Despite a significant research effort, the structure, aggregation and deposition of asphaltenes under flowing conditions remain poorly understood. For this reason, we have investigated asphaltenes, their aggregation and their deposition in capillary flow using multi-scale simulations and experiments. At the colloid scale, we use a hybrid simulation approach: for the solvent, we used the stochastic rotation dynamics (also known as multi particle collision dynamics) simulation method, which provides both hydrodynamics and Brownian motion. This is coupled to a coarse-grained MD approach for the asphaltene colloids. The colloids interact through a screened Coulomb potential with varying well depth ε. We tune the flow rate to obtain Peflow ≫ 1 (hydrodynamic interactions dominate) and Re ≪ 1 (Stokes flow). Imposing a constant pressure drop over the capillary length, we observe that the transient solvent flow rate decreases with increasing well depth ε. The interactions between the mesoscopic asphaltene colloids can be related to atomistic MD simulations. Molecular structures for the atomistic calculations were obtained using the quantitative molecular representation approach. Using these structures, we calculate the potential of mean force (PMF) between pairs of asphaltene molecules in an explicit solvent. We obtain a reasonable fit using a -1/r2 attraction for the attractive tail of the PMF at intermediate distances. We speculate that this is due to the two-dimensional nature of the asphaltene molecules. Finally, we discuss how we can relate this interaction to the mesoscopic colloid aggregate interaction. We assume that the colloidal aggregates consist of nano-aggregates. Taking into account observed solvent entrainment effects, we deduct the presence of lubrication layers between the nano-aggregates, which leads to a significant screening of the direct asphaltene-asphaltene interactions.
UR - http://www.scopus.com/inward/record.url?scp=70350233623&partnerID=8YFLogxK
U2 - 10.1039/b902305b
DO - 10.1039/b902305b
M3 - Article
C2 - 20158034
AN - SCOPUS:70350233623
SN - 1359-6640
VL - 144
SP - 271
EP - 284
JO - Faraday Discussions
JF - Faraday Discussions
ER -