Abstract:

The Chunfeng oilfield is located in the Chepaizi uplift of the northwestern margin of Junggar Basin.The heavy oil reservoir is characterized by shallow burial,multiple oil-bearing layers,high oil density and viscosity.The biomarkers generally experienced strong degradation,making it hard to perform oil-source correlation and study of oil accumulation.In this paper,we used experimental methods to analyze fluid inclusion's composition,optical characteristics,occurrence features,homogenization temperature and salinity,performed oil-source correlation,and studied the accumulation period and process.The results show that the heavy oil was mainly sourced from the Permian source rocks in the Changji Depression,and the oil has experienced a slight biodegradation before accumulation and strong degradation later.Late charging also occurs in some wellblocks.At the end of Triassic,the Mid-Lower Permian source rocks had entered into peak oil generation and the oil generated from the Permian migrated to and accumulated in the Cheguai faulted belt.The tectonic movement during the end of Cretaceous to Paleogene destroyed and reconstructed the reservoir in the Cheguai faulted belt,and the hydrocarbons migrated to the Chepaizi uplift and accumulated in the Jurassic and Cretaceous reservoirs.Because of the poor preservation conditions,the oil commonly experienced strong biodegradation and was turned into heavy oil.Since the Neogene,the tectonic movement further adjusted the reservoirs in the Cheguai faulted belt,oil and gas migrated to Chepaizi uplift and accumulated in the favorable traps in Chunfeng oilfield and was biodegraded later into heavy oil reservoir.

Key words: fluid inclusion, oil-source correlation, accumulation evolution, super-heavy oil, Chunfeng oilfield, Junggar Basin