ABSTRACT

The saturated and aromatic hydrocarbons isolated from a Cambrian oil (TZ62well) in the central Tarim basin were pyrolyzed in sealed gold tubes to investigate how the gases generated from them would vary in compositions of constituents and their carbon isotopes. The results illustrates that the gases from the cracking of saturates are much drier and more enriched in ¹²C than the gases from the cracking of aromatics at the same levels of thermal maturity. The dryness index of the gases (defined as the volume percentage of C₁ to C_1-5) from the cracking of saturates ranges from 26.2% to 90.6% whereas it is never lower than 60.6% for the gases from the cracking of aromatics throughout the experiment. The methane from the saturates shows a larger carbon isotope change, ranging from -54.8‰ to -35.5‰, than the methane from the aromatics whose carbon isotopes range from -37.4‰ to -32.2‰ throughout the experiment. The above experimental observations indicate that the cracking of crude oils with different bulk compositions could produce gases that have distinct constituents and carbon isotopic compositions.