Molecular Composition Characterization of Oilsand Heating Experiments to Investigate Steam-Solvent Effects and Chemical Reactions during Thermal Recovery

摘要

To better understand the hot-water-mediated organic transformation process that occurs during the steam-assisted recovery of heavy oil and bitumen, a series of heating experiments has been performed on Athabasca oilsand in stainless-steel tubes under isothermal conditions at temperatures of 300 degrees C for 5 and 15 days and 330 degrees C for 5 days. Compounds absent in the raw bitumen due to biodegradation were generated after heating under 300 degrees C for 5 days. Their occurrence was most likely the release of an occluded fraction from asphaltenes. Concentrations of gas chromatography (GC)amenable compounds were doubled after heating at 300 degrees C for 5 days and tripled for 15 days and were an order of magnitude higher after heating at 330 degrees C for 5 days, suggesting that both time and temperature exert significant impact on hydrocarbon release. The increased concentration of hydrocarbons can be attributed to either neoformation or relative enrichment. Molecular composition analysis illustrated that maturity parameters based on the degree of isomerization show no obvious variation under designed conditions, while ratios derived from different compound classes such as sesquiterpenes versus pentacyclic terpanes, less alkylated naphthalenes versus more alkylated naphthalenes, short-chained aromatic steroids versus longer-chained ones, and alkylnaphthalenes versus aromatic steroids can serve as a proxy for aquathermolysis reactions and degree of in situ upgrading. The free oil yield in methyl propyl ketone (MPK) addition samples is much higher than that without it, suggesting that MPK facilitates vapor transportation with steam and bitumen's mobility. However, free oil with MPK addition may be selectively enriched in polar species diluting the hydrocarbons produced. Our experimental results provide deep insight into the reaction mechanisms of heavy oil and bitumen during the thermal recovery process and a potential route for the process optimization.