Multi-scale simulation of asphaltene aggregation and deposition in capillary flow.

Area of Science:

• Petroleum Engineering
• Colloid Science
• Computational Chemistry

Background:

• Asphaltenes, complex molecules in crude oil, form nano-aggregates and precipitate, significantly reducing oil recovery efficiency by blocking pores and altering rock wettability.
• The structure, aggregation, and deposition mechanisms of asphaltenes under dynamic flow conditions remain poorly understood, hindering effective mitigation strategies.
• Understanding asphaltene behavior is critical for optimizing oil extraction and preventing operational issues in reservoirs.

Purpose of the Study:

• To investigate the aggregation and deposition of asphaltenes in capillary flow using a multi-scale simulation and experimental approach.
• To elucidate the relationship between asphaltene-asphaltene interactions and their macroscopic behavior during flow.
• To provide insights into the mechanisms governing asphaltene-induced flow impairment.

Main Methods:

• Employed a hybrid multi-scale simulation approach, coupling stochastic rotation dynamics for solvent hydrodynamics and Brownian motion with coarse-grained molecular dynamics for asphaltene colloids.
• Investigated asphaltene interactions using a screened Coulomb potential and tuned flow rates to achieve conditions where hydrodynamic interactions dominate (Pe(flow) >> 1) and Stokes flow prevails (Re << 1).
• Utilized atomistic molecular dynamics simulations with structures from quantitative molecular representation to calculate the potential of mean force (PMF) between asphaltene molecules.

Main Results:

• Observed that the transient solvent flow rate in a capillary decreases with increasing asphaltene-asphaltene interaction strength (well depth epsilon).
• Calculated PMF between asphaltene molecules revealed an attractive tail at intermediate distances, fitting a -1/r^2 potential, potentially due to their 2D molecular nature.
• Deduced the presence of lubrication layers between colloidal aggregates, significantly screening direct asphaltene-asphaltene interactions, accounting for solvent entrainment effects.

Conclusions:

• The study successfully links atomistic interactions of asphaltenes to their mesoscopic aggregation and deposition behavior in capillary flow.
• Interaction strength and lubrication layers play crucial roles in modulating asphaltene deposition and flow impairment.
• Findings provide a foundation for developing more accurate models of asphaltene behavior in porous media, aiding in enhanced oil recovery strategies.