Characterization of microscopic pore structure of transitional facies shale of Taiyuan Formation in Ningwu Basin

Take transitional facies shale of Taiyuan Formation in Ningwu Basin as an object to deeply investigate the pore structure of transitional facies shale reservoir, by means of scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) technology and low-temperature nitrogen adsorption method. Results show pores in transitional facies shale reservoir can be classified into four types: organic pores, mineral intercrystalline pores, moldic pores and microfracture.T₂ spectrum of samples are of similar features and have bimodal distribution at T₂=0.8～1ms and T₂= 20～50ms respectively .Moreover, T₂ spectrum are divided into higher-altitude T₂ spectrum and lower-altitude T₂ spectrum according to value at left peak. It is noticeable that the former samples have higher maturity and lower organic carbon content, while the latter samples are converse, indicating maturity and organic carbon content may have a role in pore structure. Low-temperature N₂ isotherm of samples are correspond to type Ⅳ and hysteresis loops are similar to type H3, partly type H2, reflecting the parallel plate-like pores. Shale fractal dimension D value calculated by FHH equation is between 2.66 and 2.71, which is close to 3, indicating that the shale pore structure is more complex, and of strong heterogeneity, which is mainly related to heterogeneity of micropores.