Relationships between SARA fractions of conventional oil, heavy oil, natural bitumen and residues

A number of indices generated from SARA analyses data are used for characterization of petroleum mixtures (e.g. colloidal instability index Ic = (As + S)/(R + A) and asphaltene index Ia = (As + R)/(S + A)). Knowledge of relationships between SARA fractions is necessary for selection of indices, understanding of chemical continuum from light to heavy compositions and prediction of properties such as density, viscosity, boiling temperature, asphaltene stability, and others. SARA analyses data of 230 samples of conventional oil, heavy oil, oil sand, natural asphalt, residues obtained through refinery processes, and bitumen blends from 50 publications are compared. For the exception of conventional oil and bitumen blends, data of SARA fractions taken in pairs follow similar lines with the slopes of k = ±1 when plotted as Y vs. X for heavy oil, natural bitumen and residues. The slope of 1 indicates that sums or differences of two fractions (±Y ± X) are constants regardless of a wide range of variation of Y and X. This allows graphic solution of indices and evaluation whether they are applicable for specific types of petroleum mixtures. The close values of (R + A) and (As + S) are more often generated for natural bitumen data, relevant to calculation of Ic. For heavy oil and residues, combinations of either (R + A) and (As + S), or (S + A) and (As + R) depend on origin. Ia has no graphic solution for conventional oil.