Abstract: Qigu oilfield is located in the southern margin of Junggar basin with complex terrain and high?steep structures, in which Karamay formation of Triassic belongs to lacustrine shoal?bar sand body sediments with wide distribution area, big thickness and some potentials for hydrocarbon exploration．Because the strata are relatively old and deep?buried in geologic history periods，they have strong diagenesis and compaction, being characterized by seldom primary porosity and developed secondary porosity and fractures. The study shows that the Karamay formation belongs to a porous medium reservoir with super-low porosity and ultra?low permeability, smaller pore throat and high displacement pressure．And it is concluded that this reservoir belongs to a non?conventional and tight sandstone reservoir