Discovery of bitumen display in Nima Basin of Tibet and analysis of oil source.

An EW-trending oil and gas display belt with 80 km length was discovered in the Saibuya depression of eastern Nima Basin, which indicating satisfactory prospect of oil and gas.Analysis of saturated hydrocarbons by gas chromatography-mass spectrometry was carried out to determine the geochemical characteristics and specific sources of the bitumen.The results show that the bitumen is in the mature stage and has not suffered significant biodegradation.It is characterized by high carbon number alkanes(> nC₂₅), lower Σ(≤nC₂₁)/Σ(≥nC₂₂)and (nC₂₁+nC₂₂)/(nC₂₈+nC₂₉), with obvious advantage of hopane ααα-20RC₂₉, which reveal the superior input of organic materials with terrigenous higher plants.The analysis of bituminous samples and comparison with the dark rock biomarkers of the Niubao Formation outcropped in Kangale show that they have a good genetic relationship, which confirms that the Nima Basin is a self-generating and self-storing continental petroliferous basin.