In order to characterize the micro pore structure of Shahezi Formation shale in Songliao Basin

nine shale samples from the lower part of the Shahezi Formation in the Songliao Basin were selected to carry out NMR

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tests in saturated and dry conditions

and simultaneous petrophysical testing with field emission scanning electron microscope observation. The

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relaxation characteristics

pore types and distribution characteristics were systematically analyzed. And the difference of porosity measured by the NMR method and the gas method was co

mpared. The results show that the NMR

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spectrum of the shale samples from the Shahezi Formation is dominated by a single peak type with shorter relaxation time

and the pore diameter is mainly distributed in the range of 10~1 000 nm. The pore types are mainly nano-scale inorganic pores

and the organic pores and microfracture generally underdeveloped. The NMR porosity calculated after deducting the base signal is 0.68 %~3.66 %

which has a good matching relationship with Helium porosity. The samples with smaller porosity are more likely to be affected by the background signal of rock matrix

resulting in the relative error of test results. In generally

the nuclear magnetic resonance technology can accurately analyze the porosity and pore size distribution of low porosity and low permeability shale samples

but attention should be paid to the NMR signal interference caused by organic matter and clay mineral bound water.