Abstract: Xinlicun oilfield located in eastern Dongying sag is characterized by normal crude associated with heavy oil which occurs mostly in structural high far from oil source. The analyses from fluid property, crude composition and geochemistry show that the heavy oil reservoir is in good condition of preservation in late period, slight microbial degradation, featuring low-maturity oils in half salt-saltwater lacustrine source rocks. The original heavy oil is resulted from low maturity and long distance migration, which reduces the lateral seal to faults and is favorable for forming reservoir. Moreover, as a kind of plugging zone, the heavy oil in this area plays an important plugging role in successively hydrocarbon accumulation.

Key words: Dongying sag, heavy oil, low maturity oil, petroleum migration