Issues with Comparing SARA Methodologies

One of the most common compositional analyses for petroleum samples is known as the SARA (saturates, aromatics, resins, and asphaltenes) fractionation test. SARA fractionation is also used as one of the screening criteria for asphaltene stability of reservoir fluids due to pressure depletion or commingling of different fluids. There are numerous variations of this type of analysis. First, the extraction of asphaltenes is not consistent from method to method. Asphaltenes are extracted using either pentane, hexane, or heptane. There are no specific reasons for selecting one over the other, and usually the users do not associate differences in results with the nature of the solvent. In addition, the extraction temperature could have an impact on the amounts of asphaltenes extracted. The fractionation of maltenes is also a challenge, usually ignored by end-users. Assuring no overlap between fractions and obtaining a very good mass balance are among these challenges. They could be impacted by the type of packing material amount of solvents used for the chromatographic separation. These SARA methods, referred to as standard methods, usually generate different results leading to confusion if the users are not that familiar with analytical details of each method. This paper discusses the role of the major parameters involved in generating the four fractions and how these parameters affect results, thus impacting decision for the end-users. It also shows that it is impossible to perform any prediction of results when changing from one method to another.