Reservoir feature of Jurassic 8th member of Yan'an for- mation in Huanchi oilfield

Situated in the middle part of the west margin of Or-dos basin, the reservoirs in Huanchi oil field belong to Jurassic Yan'an formation channel sandstone, the rock type is mainly lithic quartz sandstone, the porosity type is mainly primary and secondary, with 12% -16% porosity, the average is 12.6%, the permeability(0.5~50)×103μm2 ,the average is 11. 19×10-3μm2, the pore radius is 5-34. 91μm, the average is 32. 3μm and the average throat radius is 1. 19μm. The reservoirs in the area can be divided into four types according to the above characteristics, among whichⅠandⅡare of good reservoirs,Ⅲis of poor reservoir, andⅣis of impermeable reservoir. It is concluded from the comprehensive evaluation that the reservoir in the area is of low - porosity and low - permeability, medium-porosity and fine-throat.