Asphaltenes generally aggregate, then precipitate and deposit on the surfaces of environmental media (soil, sediment, aquifer, and aquitard). Previous studies have recognized the importance of asphaltene aggregates on the wettability of aquifer systems, which has long been regarded as a limiting factor that determines the feasibility and remediation efficiency of sites contaminated by heavy oils. However, the mechanisms/factors associated with precipitant effects on asphaltene aggregates structure, and how the precipitant effects influence the wettability of surfaces remain largely unknown. Here, we observe the particle-by-particle growth of asphaltene aggregates formed at different precipitant concentrations. Our results show that aggregates for all precipitant concentrations are highly polydisperse with self-similar structures. A higher precipitant concentration leads to a more compacted aggregates structure, while precipitant concentration near to onset point results in a less compact structure. The well-known Smoluchowski model is inadequate to describe the structural evolutions of asphaltene aggregates, even for aggregation scenarios induced by a precipitant concentration at the onset point where the Smoluchowski model is expected to explain the aggregate size distribution. It is suggested that aggregates with relative high fractal dimensions observed at high precipitant concentrations can be used to explain the relatively low Stokes settling velocities observed for large asphaltene aggregates. In addition, asphaltene aggregates with high fractal dimensions are likely to have high density of nanoscale roughness which could enhance the hydrophobicity of interfaces when they deposit on the sand surface. Findings obtained from this study advance our current understandings on the fate and transport of heavy oil contaminants in the subsurface environment, which will have important implications for designing and implementing more effective and efficient remediation technologies for contaminated sites.
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This content will become publicly available on June 21, 2024
Kinetic Experimental and Modeling Evaluations of Asphaltene Morphology and Growth Rate under Varying Temperature and Brine Conditions
The utilization of predictive mechanisms to resolve asphaltene precipitation during oil production is a cleaner and less expensive means than the mechanical/chemical remediation techniques currently employed. Existing models lack predictive success due to opposing views on temperature-asphaltene precipitation interactions. In this study, the effect of varying temperatures (40, 50, 60, 70 80 and 90 °C) and brine concentrations (0 – 5 wt.%) on the long-time kinetics of asphaltene precipitations was evaluated. A series of experiments were conducted using the filtration technique and the confocal microscopy to study asphaltene precipitation on a model oil system consisting of asphaltenes, a precipitant, and a solvent. Furthermore, the Avrami modeling technique was employed to predict the morphology, and growth rate of the precipitating asphaltenes. The experimental results suggested that temperature significantly affects asphaltene precipitation including imparting its precipitation mechanism with a cross-behavioral pattern. Asphaltene precipitation in the system displayed an initial fast kinetics upon increasing temperature. The fast kinetics observed in the early times is due to the increasing dipole-dipole interactions between asphaltene sub-micron particles stimulated by increased temperature. However, the pattern changes into slower precipitations as the time progresses upon continuous heating of the reservoir fluid. The reason is the increased solubility of the asphaltenes imparted into the model oil system upon further increments in temperature. The presence of brine in the model-oil system also enhanced the rate and precipitation of asphaltenes. The experimental data were further analyzed with the Avrami crystallization fitting model to predict the formation, growth, morphology, and growth geometry of the precipitating asphaltenes. The Avrami model successfully predicted the asphaltene morphologies, growth rates and the crystal growth geometries. The growth geometries (rods, discs, or spheres) of the asphaltenes in the model oil systems upon temperature increments, ranged from 1.4 – 3.5. These values are indicative that temperature impacts the growth process of asphaltenes in the model system causing variations from a rod-like sporadic process (1.0 ≤ n ≤ 1.9) to a spherical sporadic growth process (3.0 ≤ n ≤ 3.9). This work precisely emphasizes the impact of temperature on asphaltene precipitations under long kinetic time, thus, providing a clear pathway for developing successful kinetic and thermodynamic models capable of predicting asphaltene precipitation reliably. The accurate prediction of asphaltene precipitation will eliminate the need for the use of harmful remediation solvents like benzene/toluene/ethylbenzene/xylene (BTEX). This study is therefore a critical step in the right direction to achieving accurate predictive model evaluations of asphaltene precipitations.
more » « less- Award ID(s):
- 1932965
- NSF-PAR ID:
- 10486077
- Publisher / Repository:
- SPE
- Date Published:
- Format(s):
- Medium: X
- Location:
- The Woodlands, Texas, USA
- Sponsoring Org:
- National Science Foundation
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