STRUCTURAL FEATURES OF ALBERTA OIL SAND BITUMEN AND HEAVY OIL ASPHALTENES

Ru ion catalyzed oxidation (RICO) has been used to probe the structural details of asphaltene molecules from Athabasca bitumen. The ability of RICO to remove nearly quantitatively aromatic carbons while leaving aliphatic and naphthenic structures essentially unaffected has been exploited for the quantitative determination of the following structural features: (1) the distribution of n-alkyl chains attached to aromatic carbons with respect to chain length, total number of n-alkyl chains, and the number of carbon atoms in them; (2) the distribution of polymethylene bridges connecting two aromatic units with respect to bridge length, total number of bridges, and the number of carbon atoms in them; (3) the fractional amount of total sulfur present as saturated sulfides. Moreover, semiquantitative estimation could be made of the carbon in bridges connecting an aromatic to a naphthenic ring and of the aliphatic carbon attached to naphthenic rings. The various isomeric benzene di-, tri-, and tetracarboxylic acids produced from the condensed aromatic nuclei during RICO gives some insight into the mode of aromatic condensation in the asphaltene molecules, clearly establishing the absence of pericyclic aromatic structures. RICO also made possible the detection of the presence, and estimation of the quantity of n-alkanoic acid esters anchored to the aliphatic/naphthenic cores of the asphaltene molecules. On pyrolysis these esters give rise to n-alkanoic acids which are characterized by a short carbon range up to approximately C22, high even carbon number preference, and the presence of small quantitites of C18 unsaturated n-alkanoic acids, linking their origin to relatively recent microbial activities in the reservoir. The RICO of asphaltene also shows the existence of large aliphatic/naphthenic domains in the asphaltene, with MW up to approximately 8700. RICO studies of asphaltenes from various Alberta oil sands and carbonate bitumens and a heavy oil reveal close structural similarities among these asphaltenes, which in turn point to a common origin for these huge oil accumulations.