Abstract
Abstract A series of C26 norcholestanes was detected in the Ordovician crude oils from the Tahe Oilfield, the Tarim Basin, northwest China. The abundance of 24-norcholestanes in most of the Ordovician crude oils was lower than that of 27-norcholestanes. The oils from well T904 in the eastern Tahe Oilfield and well TD2 in the eastern Tarim Basin, however, were characterized by relatively higher 24-norcholestane abundance. The distribution of C26 norcholestane of the Upper Ordovician marls from the wells LN46 and BD2 resembled that of the most Ordovician crude oils from the Tahe Oilfield. The distribution of C26 norcholestanes in typical Cambrian black shales and gray limestones from the wells TD2, He4 and outcrops from Keping profile resembled that of the crude oils from the wells T904 and TD2. Criteria are proposed relative to C26 norcholestanes that could be used to classify oil families within the Ordovician reservoirs. Oils with NCR (defined as 24/ (24+27)-norcholestanes) >0.50 and NDR (defined as 24/ (24+27)-nordia-cholestanes) >0.35 were thought to be derived from the Cambrian source rocks, and oils with NCR<0.40 and NDR<0.35 were thought to be derived from the Upper Ordovician source rocks. Therefore, C26 norcholestanes were effective molecular markers to classify oil genetic families in the Tahe Oilfield. They could also provide molecular evidence for the origin and evolution of diatoms and dinoflagellates and the plate drift of the Tarim Basin.
Highlights
A series of C26 norcholestanes was detected in the Ordovician crude oils from the Tahe Oilfield, the Tarim Basin, northwest China
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Summary
A series of C26 norcholestanes was detected in the Ordovician crude oils from the Tahe Oilfield, the Tarim Basin, northwest China. Holba 等[2,3] 的研究表明,尽管 NCR [24 / (24+ 27) -降胆甾烷] 在三叠纪以前较低(
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