Abstract:

Oil samples from Dawanqi Oilfield in the Tarim Basin, NW China, that have been biodegraded to various degrees were
analyzed to study the effect of biodegradation on light hydrocarbons. The results show that biodegradation led to preferential depletion
of n-alkanes, followed by iso-alkanes and cycloalkanes, which results in variations in the corresponding C6 and C7 ternary diagram. With
increasing biodegradation, the values of n-heptane and isoheptane decrease, ratios of toluene/n-heptane and benzene/n-hexane increase,
and n-heptane/methylcyclohexane ratio decreases. In Dawanqi Oilfield, the crude oil with heptane values of 0~21 and isoheptane
values of 0~2.6, is categorized as“Biodegraded”zone. The graph of toluene/n-heptane versus n-heptane/methylcyclohexane indicates
that secondary alterations should be applied with caution in slightly biodegraded crude oil.

Key words: Light hydrocarbon parameters, Biodegradation, DawanqiOilfield, Tarim Basin