Progress toward Thermodynamic Models of Asphaltene Solubility

Jill S. Buckley

PRRC, New Mexico Tech, Socorro, NM, USA

ABSTRACT

Progress in asphaltene research has been slow, measured not in years but in decades.  Gradually, new tools have emerged and older tools have been reinterpreted.  This keynote will begin with a review of some recent advances and try to identify specific obstacles—both real and perceived—that remain as challenges to asphaltene researchers. 

A complete model of asphaltene phase behavior should include the separations that occur at ambient conditions in the presence of paraffinic diluents, changes in phase behavior that occur upon addition of aromatic solvents, and the phase separations from live oil that can occur with changes in pressure and temperature.  Too often researchers have focused only on one or another of these regimes.  It is time to move beyond our narrow perspectives to a broader view of asphaltenes and their solubility in crude oil.

Thermodynamic approaches to describing asphaltene stability are not new, but acceptance has been slow.  In a system as complex as a crude oil, many simplifying assumptions must be made in order to write and solve equations that describe the system.  Finding a set of assumptions that make the problem tractable, without sacrificing predictive capability, is an ongoing effort.  Precipitation onset conditions can be predicted by describing the crude oil mixture with as few as two components, but more detailed characterization is required to predict the amount of asphaltene-rich phase that separates beyond the onset condition.  There is as yet no agreement on what those detailed characterizations must include or how to measure the requisite data.  Until these questions are answered, efforts at standardization will remain premature.  Nevertheless agreement on standard methods must eventually emerge if predictions of asphaltene-related phenomena are ever to gain widespread credibility.