Abstract
The east edge of Chepaizi High belongs to the western slope belt of the southern Junggar foreland basin, NW China. Based on the features of oil source and migration pathway, this study rebuilt the charging history of crude oils related to the slope belt reservoir forming in the east edge of Chepaizi High, comprehensively through the methods of fluid inclusion microscopic observation, microthermometry and microbeam fluorescence spectra. The results show that there are mainly 4 periods of oil charging including the Middle Jurassic to the Middle Cretaceous (the 1st period), the Middle-Late Cretaceous to the Early Paleogene (the 2nd period), the Early Neogene (the 3rd period) and the Middle-Late Neogene to the Quaternary (the 4th period). The 1st and 2nd period oils both generated from the Permian Wuerhe source rock charged into the Mesozoic reservoirs. The 1st period oil is low-mature to mature with long time and large-scale volume of oil charging, while the 2nd period oil was mature to highly mature with short time and small-scale volume of oil charging. Partial 1st period oil suffered biodegradation because of poor preservation conditions resulted from tectonic uplift in the Late Jurassic. In the Early Neogene, biodegraded oil gradually migrated into the shallow reservoirs and formed the secondary heavy oil reservoirs as the 3rd charging period. The 4th period oil was mainly from the Jurassic source rock. Through the migration pathways composited by sand bodies, faults and unconformities, the oil migrated into the Neogene Shawan reservoirs and formed the light oil reservoirs. Meanwhile, the oil was overprinted by some low maturity Cretaceous organic matter during upward migration, and some oil from the Jurassic source rock got mixed with the earlier charging heavy oils. For different tectonic evolution stages, there existed distinct oil charging characteristics in the study area.
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