Abstract: Jurassic abnormally high pressure zones were discovered at a depth 4 500 m and 5 700 m of Well Pencan 2 in Mosuowan area of hinterland of Junggar basin. This paper discusses the origins of abnormal formation pressure, based on the theory on formation of abnormal formation pressure, organic theory and the model of hydrocarbon Zonation. It is suggested that the lithologic seal is the prerequisite, release of abundant interformational water from clay minerais during katagenesis petriod and lower maturation phase of Lower Jurassic source bed resulted in increase in fluid temperature and pressure，and then abnormally high pressure as well as a temperature-active zone were establish. Controlled by the temperature and pressure conditions, oil/gas zonation conspicuously occurs in exploration target zone(Jurassic); oil accumulation zone and condensate or natural gas accumulation zone exist above and beneath the seal, respectively. Finally, it is concluded that the Jurassic underlain by the seal at 4 500m should be considered to be main candidatc for exploration.

Key words: Hintcrland of Junggar basin, Well Pencan 2, Abnormal formation pressure, Oil/gas zoning, Geologic risk evaluation