The conventional well log evaluation is a challenge for geologists and well log analysts in low permeability sandstones at present due to the effect of the complicated pore structure. In this paper, based on the analysis of the laboratory NMR measurements, core experimental mercury injection capillary pressure data, the casting thin-section and the drill stem testing data, the effects of the pore structure to low permeability sandstones can be conclude to form three different types of low contrast hydrocarbon bearing formations, they are low resistivity contrast of gas bearing formations with water saturated layers, the low porosity and permeanility contrast for effective formation with dry layer and the low porosity and resistivity contrast of formations with high productivity layer and low productivity zone. To evaluate low permeability reservoirs responsibly, the information of pore structure should be first obtained.

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