(58f) New Asphaltene Nanoscience and Its Impact on Reservoir Characterization

Asphaltene science has undergone a renaissance in recent years with many of the advances being subsumed in the “modified Yen model” which consists of asphaltene molecules, nanoaggregates and clusters of nanoaggregates. Various molecular diffusion and mass spectral measurements show that asphaltene molecular weights are ~750 (range 500-1000) Daltons. Molecular diffusion measurements originally established the predominance of one polycyclic aromatic hydrocarbon (PAH) per molecule; this is now supported by unimolecular decomposition studies. This molecular architecture yields nanoaggregates with <10 aggregation number. High-Q ultrasonic studies were first to show that asphaltene nanoaggregates form at 10^-4 mass fraction. SANS and SAXS studies show small stable asphaltene nanoaggregates; DC-conductivity studies support all these findings of the size and aggregation concentration. Clusters form at ~10^-3 mass fraction as shown by a flocculation kinetics and other measurements. Surface studies of molecular orientation and surface morphology dependence on aggregation are consistent with the modified Yen model. The combination of this new asphaltene nanoscience with new technology of performing chemical measurements in situ in oil wells is proving of enormous value in the oilfield reservoir evaluation. Depending on asphaltene concentration, all three forms, molecules, nanoaggregates and clusters are found in reservoirs. The new asphaltene nanoscience has given rise to the industry’s first predictive equation of state for asphaltene gradients; in turn, this aids in charactering reservoir connectivity, heavy oil, tar mat formation and fluid disequilibrium. New science combined with new technology provides powerful new solutions to key problems.