The Role of Asphaltene Solubility and Chemical Composition on Asphaltene Aggregation

Abstract

Abstract Abstract Asphaltenes from four different crude oils (Arab Heavy, B6, Canadon Seco, and Hondo) were fractionated in mixtures of heptane and toluene and analyzed by small angle neutron scattering (SANS). Fractionation appeared to concentrate the most polar species into the least soluble sub-fraction as indicated by elemental analysis. SANS results indicated a wide spectrum of asphaltene aggregate sizes and molecular weights; however, the less soluble (more polar) fraction contributed the majority of the species responsible for asphaltene aggregation in solution. This more polar, less soluble fraction is likely the major cause for many petroleum production problems such as deposition and water-in-oil emulsion stabilization. A comparison of molecular weight and aggregate size indicated that asphaltenes formed fractal aggregates in solution with dimensions between 1.7 and 2.1. This was consistent with the “archipelago” model of asphaltene structure. Resins were shown to effectively solvate asphaltene aggregates as observed by an increase in asphaltene solubility, reduction in aggregate size and molecular weight, and an increase in the fractal dimension to ˜ 3. Acknowledgments We are grateful to the National Science Foundation (grant CTS-981727), the Petroleum Environmental Research Forum (contract 97-07), and shared consortium funding from ExxonMobil, Texaco, Ondeo-Nalco Energy Systems, and Shell Oil Company for partial support of this research. Special thanks go to George Blankenship, Marit-Helen Ese, Jihong Tong, Chad Trail, and Semaj McIver who assisted with the experimental work. We are also grateful to Eric Sirota and Min Lin of ExxonMobil Research and Engineering for arranging beamtime at the NIST NG-7 and NG-1 beamlines for the SANS experiments, and to Thiyaga Pappannan and Dennis Wozniak at Argonne National Laboratories (SAND beamline) for arranging and assisting with beamtime there.