Effect of the Amount and the Composition of Precipitated N-Alkanes on the Yield Stress of Wax-Decane Gels

Asphaltenes represent the heaviest fraction of the crude oil. The physical and chemical variations occur during oil production destabilize the asphaltene molecules and cause asphaltene precipitation. This work deals with the analysis of the change in asphaltene phase behavior due to compositional variations within crude oil. Two crude oil samples which have different asphaltene content, API gravity, and viscosity were examined. The stability of asphaltenes was investigated by defining each crude with four-component system. Hence, the crude oils were divided into their Saturates, Aromatics, Resins, and Asphaltenes (SARA) fractions by following a standard method which uses n-pentane to separate asphaltenes. First, the spectral characterization on the crude oils and on their SARA fractions was achieved by Fourier Transform InfraRed (FTIR) spectroscopy. Then, the quaternary phase diagrams were constructed by using the pseudo blends of SARA fractions at varying amounts. The two-phase (solid-liquid) envelope has been formed. The resins to asphaltenes ratio is the key to asphaltene stability. Moreover, asphaltenes are soluble in aromatic solvents and insoluble in normal alkanes, thus, while the increase in saturates fraction in crude oil decreases the asphaltene stability, the increase in 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. The systematic analyses conducted in this study enhance our understanding towards asphaltene stability mechanism. The role of deasphalted crude oil fractions on asphaltene stability is described.