Determination of saturate, aromatic, resin, and asphaltenic (SARA) components in crude oils by means of infrared and near-infrared spectroscopy

Eighteen crude oils and condensates have been investigated by means of infrared (IR) and near-infrared spectroscopy (NIR) and high-performance liquid chromatography (HPLC). By means of HPLC the samples have been separated into four chemical group classes, namely saturates, aromatics, resins, and asphaltenes, the so-called SARA fractions. Using multivariate analysis techniques such as principal component analysis (PCA) and partial least-squares analysis (PLS), the predictive ability of the spectroscopic techniques with regard to the SARA components have been explored. The results show that the SARA distribution of crude oils and related materials can be determined both from infrared and near-infrared spectroscopy. The uncertainties in the prediction models based on IR spectroscopy have been found to be 2.5, 2.2, 1.4, and 1.3 wt % for the saturate, aromatic, resin, and asphaltene fraction, respectively. For NIR the equivalent uncertainties are 2.8, 2.4, 1.4, and 1.0 wt %. These values are in the same range as the reported uncertainty in the direct determination by HPLC. Spectroscopic determination of SARA values, especially using NIR, offers the possibility of rapid SARA determinations of these values. The determinations could be done at high pressure and temperature.