Asphaltene characterization of paraffinic crude oils

• Analyses of solid phases from paraffinic oils revealed the presence of asphaltenes.
• Asphaltenes with large solubility parameters precipitate together with waxes.
• Asphaltenes in deposits show larger solubility parameters than ones in the oil.
• Composition of precipitated asphaltenes changes as a function of time.

Precipitation and deposition of asphaltene and waxes pose a serious challenge to the petroleum industry since costly remedial actions to maintain operations are required. Even though asphaltenes and waxes are radically different in chemical nature, they both have low solubility in crude oils, and they frequently appear together in recovered deposits from wells and pipelines. In this work, we evaluate the solubility characteristics of the asphaltenes that are naturally associated themselves with the wax crystals present in several paraffinic crude oils. Filtration was used to separate precipitated waxes from crude oils at room temperature, and the solubility distributions of asphaltenes associated with the precipitated waxes are compared with the distributions of the total asphaltenes present in the original crude oils. It was found that the filtered cakes were enriched in the least soluble asphaltenes as indicated by their larger average solubility parameters in comparison with the crude oil (21.3–21.6 MPa0.5 vs. 18.5–18.6 MPa0.5). These are the type of asphaltenes likely to be present in deposits together with waxes. Additionally, after filtration, the filtered crude oil was spiked with pentane asphaltenes and after one week, the precipitated solids were separated again and analyzed. The results indicated that the precipitated solids were enriched in higher solubility parameter asphaltenes in comparison to the pentane asphaltenes originally added. This separation is likely the product of the low solvent power of the maltenes of these crude oils. Comparison of the precipitated asphaltenes from original and spiked crude oils revealed that those that precipitated in association to wax crystals had larger solubility (21.3–21.8 MPa0.5 vs. 20.0–20.1 MPa0.5) parameters than those recovered after spiking.