%0 Journal Article
%J Energy & Fuels
%D 2008
%T Identification and Characterization of Reaction Proxies for Monitoring the Progress of Thermal Processing of Heavy Oils and Tar Sands under Visbreaking Conditions
%A Bennett, B
%A Larter, S
%A Carbognani, L
%A Almao, Pereira
%K reaction proxies, thermal processing, visbreaking
%P 440-448
%V 22
%X <p>  The vacuum residue prepared from Athabasca bitumen was heated at 380°C for up to 5.5 hours under vis-breaking conditions. The level of conversion was indicated by weight loss due to generation and removal of light ends from thermal cracking reactions. Classical molecular parameters that are commonly applied to indicate the level of thermal maturity of petroleum source rocks during burial maturation have been investigated towards indicating the extent of bitumen conversion under vis-breaking conditions. The molecular parameters known to monitor chemical reactions such as; isomerisation, carbon-carbon bond cracking and aromatization showed strong correlations with the level of conversion during vis-breaking. The reaction mechanisms based on simple precursor-product relationships appear inherently more complex when quantitative molecular data is considered. For example, the concentrations of C28 (20S + 20R) tri-aromatic steroid hydrocarbons show an 80% loss at 30% conversion, while C20 tri-aromatic steroid hydrocarbons increase only slightly. The change in the tri-aromatic steroid parameter C20 / (C20+C28S+C28R) are controlled by the apparent relative stabilities of C28 versus the C20 compounds. In view of the strong correlations between changes recorded in the classical molecular parameters and increasing thermal stress, the parameters may be suitable for application as reaction proxies to probe reaction conditions attained during in-situ upgrading of heavy oil and tar sands in the subsurface.   </p>