Abstract:

Chepaizi uplift lies between Changji sag and Sikeshu sag, which is a favorable area for oil accumulation with abundance oil sources and favorable structures. During recent years, many new oil fields were found in the southwest of Chepaizi uplift. By 2004, the oils had been discovered from the Jurassic, Cretaceous and Tertiary in the study area. Geochemical features of oils or core extracts are analyzed from these reservoirs. It is concluded that these oils can be divided into two groups. The first group is subjected to biodegraded heavily and two stages of hydrocarbon accumulation are predicted. In the first stage oils from Permian were biodegraded, and in the second stage oils were derived from Jurassic. The second group are the mixtures of Jurassic coal-formed oils and Cretaceous-derived oils. The carbon isotope, n-alkanes and isoprenoids compositions of these oils are similar to core extracts from Jurassic coal measures. However, sterane and terpane compositions of these oils show affinity to Cretaceous source rocks. It is deduced that coalformed oils dissolved the biomarker-rich Cretaceous bitumen of relatively low thermal maturity, and overprinting occurs during oil migration.

Key words: Junggar Basin, Chepaizi uplift, oil geochemical feature, oil-sources correlation, reservoir overprinting