A New Approach to Determine Asphaltenes Stability
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AbstractAsphaltenes stability is a phase behavior phenomenon and affected mainly by the change in pressure and temperature. However, the changes in pressure and temperature lead compositional changes, hence, the dependency of asphaltenes stability on crude oil composition requires more clarity. In this study, the impact of solubility, polarity, and reservoir rock composition on asphaltenes stability for 11 different crude oil samples were investigated. All crude oil samples used in this study due to their high viscosity and low API gravity were classified as heavy oil, extra-heavy oil, and bitumen. Samples were first separated to their Saturates, Aromatics, Resins, and Asphaltenes (SARA) fractions. Based on the obtained weight percent of SARA fractions, solubility of asphaltenes in crude oil fractions was determined through Colloidal Instability Index (CII). Polarity of the crude oil samples was indirectly defined by dielectric constant measurements. Finally, the asphaltenes fractions was mixed with deionized water and then the supernatant samples were analyzed in terms of Total Dissolved Solids (TDS) and zeta potential to observe the possible interactions between reservoir rock and crude oil. Our results suggest that reservoir rock-crude oil interaction affects most the asphaltenes stability. Moreover, this interaction has positive impact on maintaining asphaltenes stability. As the asphaltenes interact more with the reservoir rock, in general, asphaltenes surfaces become negatively charged, consequently, the electrostatic repulsions created by the reservoir rock components attached to the asphaltenes surfaces keep the asphaltenes clusters apart. If the inorganic-organic interaction (reservoir rock and crude oil interaction) is insignificant, then, asphaltenes stability is determined by polarity and solubility.
