Kinetic Experimental and Modeling Evaluations of Asphaltene Morphology and Growth Rate under Varying Temperature and Brine Conditions

Abstract

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.