FORMING MECHANISM OF HYDROCARBON POOLS IN TAHE OILFIELD OF THE NORTHERN TARIM BASIN

High temperature GC analysis of high molecular weight hydrocarbons (HMWHCs) was performed on marginal mature source rock extractions from the Shahejie Formation, Damintun Depression, whose oil is particularly rich in wax. Organic composition and depositional environment are the main control factors for the formation of HMWHCs. The main maceral components in organic-rich samples (TOC>3.0%) are liptinite and exinite, deposited in relatively reduced environment. They contain high amount of waxes but dominated by macrocrystalline ones (centred at C₂₉). Those organic-lean samples (TOC<2.0%) are dominated by vitrinite, deposited in a slightly oxidized environment. They contain lower amount of waxes but relatively rich in microcrystalline components. Besides normal alkanes, high amounts of branched/cyclic hydrocarbons have been detected in the region above C₅₀.