Evaluation of Asphaltene Stability of a Wide Range of Mexican Crude Oils

Appropriate prediction of asphaltene stability can anticipate operational problems such as plugging of lines and process equipment (pumps, heat exchangers, separation tanks, among others), thus assuring the production, processing, transportation, and storage of petroleum. In the present study, the physical and chemical properties of a series of Mexican crude oils with American Petroleum Institute (API) gravity ranging from 10 to 52 were determined. Based on saturate, aromatic, resin and asphaltene (SARA) analysis, the following indexes were calculated: colloidal instability index, colloidal stability index, Stankiewicz stability criterion, stability cross plot, and oil compatibility model. The stability of crude oils was also evaluated by means of experimental techniques such as spot test, S-value, and static stability test column. No uniform results were obtained when determining the stability of crude oils with different methodologies. Due to the discrepancies disclosed, it is recommended to evaluate stability by various methodologies to adequately predict the stability of asphaltenes in crude oils. Hence, the stability of asphaltenes in a given crude oil may be ascribed based on the average result. However, from a practical point of view, pertinent cautions on the handling of samples must be observed if at least one of the methods classifies the sample as unstable or metastable.