Complex molecular structure, high impurity content, and self-association tendency of asphaltenes make the determination of their phase behavior very difficult. Because asphaltene phase behavior is indicative of asphaltene stability within the bulk oil, it is very important to understand its stability. Various production and flow assurance challenges related to precipitation of unstable asphaltenes can be prevented by proper comprehension of asphaltene stability. This study provides a data set on 11 different asphaltenes, which helps us to understand the complicated nature of the components of asphaltenes and crude oils that play an important role in maintaining the stability of asphaltenes. In addition to the physical and chemical characterizations, elemental analysis and ΔPS parameter, which is the indication of the solubility of asphaltenes in different solvents of the bulk oil samples, were measured and evaluated. The results of this study show that the presence of paraffinic wax and water within the crude oil samples along with impurities in the form of reservoir fines can greatly affect the stability of asphaltenes. The organometallic content of crude oil destabilizes asphaltenes, whereas a high fine content increases the stability of asphaltenes.

Asphaltene precipitation can severely hamper the petroleum extraction by plugging the pores or precipitation in production lines. Although the effect of temperature and pressure on asphaltene deposition is well known, how the variations in oil composition affect the asphaltene precipitation mechanism requires more clarity. This work investigates the effect of compositional changes on asphaltene stability. The impact of oil composition is explained by preparing pseudo-components by blending the crude oil with their own saturate fractions. A systematic characterization of 11 different bitumen and crude oil samples is carried out on the basis of their density, viscosity, asphaltene content, and asphaltene composition. n-pentane is used to determine the asphaltene content of each sample by following a standard method. The asphaltene composition is then determined with Fourier Transform InfraRed (FTIR) spectroscopy. The asphaltene stability is tested by performing the onset asphaltene precipitation (OAP) tests. The results from the characterization study indicated that there is no direct relationship between the asphaltene content and the density or the viscosity of the bulk samples. However, the FTIR profiles suggest that the polarity of the asphaltene molecules greatly influence the size of the precipitated clusters. The outcomes from the OAP tests were used to decipher the thermodynamic equilibrium state on the mechanism of asphaltene destabilization as per the change in the polar (resins and asphaltenes) to nonpolar (saturates and aromatics), saturates to aromatics, and resins to asphaltenes fraction of the bulk sample. It was observed that the increase in saturates concentration destabilized the asphaltene molecules and resulted in more precipitation. The presence of polar functional groups, as observed from the FTIR of the saturate fraction are believed to cause higher asphaltene precipitation. During oil production, the temperature and pressure changes can lead to asphaltene deposition and alteration in the crude oil chemical composition. A holistic understanding of the thermodynamic equilibrium corresponding to these changes can be achieved by analyzing asphaltene destabilization or restabilization processes, specifically by changing the saturate concentrations. These results are extremely useful to comprehend the asphaltene stabilization mechanism and can improve the accuracy of existing asphaltene models.

Asphaltenes and resins are the polar and saturates and aromatics are the nonpolar fractions of the crude oil. The mutual interaction within crude oil fractions results in different overall polarity. With the onset asphaltene precipitation, the overall polarity starts to change drastically and this change affects the asphaltene stability more. This study investigates the crude oil fractions polarity and their individual impact on asphaltene precipitation. Two crude oil samples with different asphaltene content, API gravity, and viscosity were divided into their Saturates, Aromatics, Resins, and Asphaltenes (SARA) fractions. The crude oils and their SARA fractions were characterized by Fourier Transform InfraRed (FTIR) spectroscopy. The polarity of crude oils and their SARA fractions were determined through dielectric constant measurements by in-house-built capacitance. The polarity of the individual fractions and bulk crude oil samples were analyzed together to understand how the mutual interaction of crude oil fractions affects the asphaltene stability. The overall polarity of the crude oil is the key to asphaltene stability. Resins and asphaltenes are the polar components of crude oil, thus, resins to asphaltenes ratio affects the overall stability of the asphaltenes. Asphaltenes are soluble in aromatic solvents and insoluble in normal alkanes, thus, while the increase in the saturates fraction in crude oil decreases the asphaltene stability, the increase in the aromatics fraction in crude oil reestablishes the stabilization. The solvent power of saturates and aromatics fractions are controlled by the impurities in saturates and aromatics fractions. Because while saturates and aromatics are known as nonpolar fractions of crude oils, the impurity content of those fractions results in polar sides in both saturates and aromatics fractions. The polar side of those fractions makes the interaction with asphaltenes more pronounced and affect the stability of asphaltenes considerably. The holistic understanding of the asphaltene stability is achieved by analyzing the polarity of asphaltenes alone and within crude oil. These results are very useful in preventing the asphaltene precipitation and modelling its stability.

Summary Asphaltenes precipitation within reservoir pores or production flowlines can severely hamper the petroleum-extraction process. Although the effect of temperature and pressure on asphaltene deposition is well-known, the manner in which the variations in oil composition affect the asphaltenes-precipitation mechanism requires more clarity. This work investigates the effect of crude-oil compositional change on asphaltene stability. The impact of oil composition is analyzed by preparing pseudocomponents through blending the crude oil with their own saturates fractions. A systematic characterization of 11 different bitumen and crude-oil samples was carried out by density and viscosity measurements and the determination of the elemental composition and saturates, aromatics, resins, and asphaltenes (SARA) contents. Further analyses were conducted on the asphaltenes separated by use of n-pentane. The cluster size was determined by a particle-size analyzer, and the stability of asphaltenes was evaluated by zeta-potential. The molecular structure of SARA fractions and bulk crude-oil samples was analyzed by Fourier-transform infrared (FTIR) spectroscopy. Onset-of-asphaltenes-precipitation (OAP) tests on crude-oil samples were achieved by the addition of different solvents (n-pentane, n-heptane, and crude-oil saturates fraction). While the physical characterization studies could only provide weak relations between the density/viscosity and the asphaltene content of the bulk samples, it has been found that mainly the ratio of the heavy (resins + asphaltenes) to light (saturates +aromatics) fractions controls the viscosity and the °API value of the crude oils. As this ratio increases, the crude oil becomes more viscous and dense. Also, the asphaltene/resin ratio was found to be critical because of its impact on asphaltene stability, which was determined through zeta-potential measurements. The high asphaltene/resin ratios result in low asphaltene stability; however, this effect is surpassed by the higher aromatics fraction in the bulk oil. Asphaltene stability was further studied with OAP tests. The OAP-test results provide the behavior of asphaltenes after the interaction of bulk oil samples with normal saturated hydrocarbons; however, our study improves the OAP-test procedure by conducting OAP tests with crude oil's own saturates fractions. The interaction of saturates fraction with crude oil resulted in more asphaltenes precipitation compared with interaction of n-pentane and n-heptane. The FTIR analyses indicate the presence of impurities in saturates fractions, and these impurities are believed to cause higher asphaltenes precipitation as a result of the polar nature of the impurities.