Abstract: Yili basin is a Mesozoic and Cenozoic intermontane basin developed in Late Hercynian folded basement with Jurassic as its host. The whole waters in Jurassic basin is shallow and unstable except for local stable waters in Badaowan formation sedimentary period of Early Jurassic, which is characterized by anastomosing stream, alluvial fan and fan-marginal braided river swamp facies; commonly poor quality of hydrocarbon source rocks in the coal measure strata with most medium hydrocarbon source rocks as dark mudstone and carbonic mudstone. From Mesozoic to Cenozoic, the basin lies in terrestrial heat flow setting of de-heating area with constant increase in crust thickness, belonging to typical “cold basin", along with organic matter thermal evolution ranging from non-matunity to low maturity (R.=0.4% -0.7%). Because of limited oil generated from low maturity dark mudstone, component content during early hydrocarbon generation of coal bed in which generated hydrocarbons are only saturated with its micropores, early hydrocarbon flow rate has little contribution to formation of reservoirs. It is pointed out that the future exploration should focus in central subsiding area, seleet optimum traps in structural belt around the hydrocarbon generation center with caution. Also, we should make further study of the hydrocarbons generated conditions and quantitative evaluations of the mudstone with low maturity.

Key words: Yili basin, Jurassic, Coal measure, Source bed, 0il and gas exploration, Organic matter, Composition, Low maturation crude oil