| Forty-six crude oil samples were selected from the Ordovician in the northwestern part of the Tahe oilfield for detailed molecular
geochemical and isotopic analysis, including group compositions, carbon-hydrogen isotopes and gas chromatograms of saturated
hydrocarbons, as well as the characteristics of terpane, sterane and other biomarkers, indicating that crude oils are of the
same origin from different districts in the Tahe oilfield and were derived from the same source kitchen (or oil source formation),
i.e., mainly stemming from marine hydrocarbons. Detailed studies of oil physical properties of 25-honpane revealed that such
oils have heavy or thick oil qualities due to biodegradation. Comprehensive assessment in terms of five maturity parameters
shows that the oils from the Ordovician with R
∘ values varying from 0.80% to 1.59% are widely distributed in the northwest of the Tahe oilfield. |
