It is obviously important to have standard asphaltene methods for comparing and classifying different crudes, heavy oils and bitumens.  Existing methods such as ASTM D6560/IP143, based on operational definitions are well known, and are useful provided that laboratories are proficient (i.e. ISO accredited) and follow the methods without deviation.  Statistical quality assurance techniques such as quality control, sample charting, participation in interlaboratory crosscheck programs such as Alberta Research Council’s crude oil exchange, and analysis of certified reference materials are essential to improving test method precision.

As mentioned already as a common theme in these discussions, the most pressing issue is whether the asphaltenes (organic solids) drop out of solution in field situations.  For example, Athabasca bitumen has a high asphaltene (n-pentane insolubles) content, but these asphaltenes are relatively compatible with the oil, which is probably why bitumen has a high asphaltene content in the first place.  On the other hand, some crudes such as those containing wax, have very low asphaltene contents, but are incompatible which can result in large asphaltene precipitation problems.  By analogy this is probably why these oils are naturally low in asphaltene content.  These facts are consistent with Per Fotland’s seemingly contradictory statement that oils with zero asphaltene content can give asphaltene problems.  Therefore, in these extreme cases the operational definitions of asphaltenes merely provide a means to classify the different oils.  They may be useful in terms of estimating the upgrading potential of the oils, but tell us nothing about what may happen during recovery, crude processing and transportation.  

An added complication already alluded to above arises when a crude contains asphaltenes and wax.  In these cases, even though it may be possible to devise methods to separately quantitate wax and asphaltenes, does it really matter?  It may matter if the intent is to determine the carbon number distribution of the n-paraffins in the wax; however, from the point of view of organic deposition it probably doesn’t.  Again it is the conditions under which organic deposition occurs, which in this case will be a waxy asphaltene solids or an asphaltenic wax solid.  These experiments may be preformed on a laboratory scale or pilot scale using flow loops.  In either case the information should be relevant to field situations and lead to possible remediation techniques.

If we choose to abandon the asphaltene definition altogether, we might consider the intriguing idea of solubility fractions suggested by Boduszynski.  This technique separates high vacuum residues into a series of fractions using solvents of increasing polarity.  While this method was originally developed in order to obtain boiling point curves to 1400°C, important for refining and upgrading, it does provide possibilities for further characterization of heavy organic deposit material.

Bryan Fuhr and Dan Wispinski
Fuels&Lubricants Group
Alberta Research Council