Origin and Geochemical Characteristics of Ordovician Oils from Tazhong Uplift

Key words: 
• Tarim Basin /
• Tazhong Uplift /
• Ordovician oils /
• origin

Abstract: Ordovician of Tazhong Uplift had abundant petroleum resources, and was main exploration Formation in the Tarim Basin. However, the origin of oils was the probleum which bothered the oil explorers all along. By systematic geochemical analysis of Ordovician oils in Tazhong Uplift, the paper discriminated oils into populations and determined their origins. Most of oils belong to light oils, light hydrocarbon shows that oils were generated in oil generating window and oils were not cracked in large amount. According to biomarker, the oil can be discriminated into three populations, one population originated from MiddleUpper Ordovician source rocks, the other population originated from Cambrian source rocks, and the third population had mixed origin. All the oils had higher content of dibenzothiophene and lower content of dibenzofuran in relative composition of Fluorinedibenzofurandibenzothiophene. Carbon isotope of saturate and aromatics in oils were lighter than -31.2‰ and -30.4‰, separately, which were apparently lighter than Cambrian oils from wells of Tadong2 and Tashen1. It shows that oils with heavier carbon isotope came from Cambrian source rocks, but oils with lighter carbon isotope came from Cambrian source rocks or MiddleUpper Ordovician source rocks.