Abstract: Jurassic coal-bearing formation scatters over the northwestern China. The low- permeability sandstone reservoir occurs as the main reservoir type. This paper analyses the genetic mechanism and reservoir property of the low permeability sandstone reservoir in the coal-bearing strata of Xishanyao formation(Lower Jurassic),Santanghu basin, Xinjiang and summarizes the regular distribution of favorable entrapment zones. The results indicate that the sands in the coal-bearing strata initially have better reservoir quality, but the severe compaction and kaolinite cementation result in the reduction of porpermea perties of reservoir sands. The coal-bearing strata have a dual impact on the pore evolution, i.e. it supports the pore destruction in the early diagenetic process and favors the formation of secondary vulgar pores in the late diagenesis. The pore type is dominated by residual primary intergranular pore, intergranular vulgar pore, interquartz micropore and fracture with the reduced-neck, silm, fine tube and cluster pore throat occurring as the main throat type. There are two basic pore texture types:large pore with fine throat(medium porosity low pemmeability and low porosity low-permeability reservoirs) and small pore with microthroat(medium-porosity extra-low permeability reservoirs). The favorable entrapment zone of the coal-bearing strata is mainly distributed in the deeply-buried area with thick source rock,coarse facies belt and fresh water leaching area below the unconformity.

Key words: Xinjiang, Santanghu basin, Jurassic, Coal-bearing strata, Low permeability reservoir, Sandstone reservoir, Sands origin, Reservoir characteristics