Experimental study on the nuclear magnetic resonance of shale in the southeastern Ordos Basin

The shale gas resource in the southeastern region of Ordos Basin has a broad development prospect,and it is of significance to accurately evaluate the different characteristics of multiple layers in shale gas reservoirs. By means of nuclear magnetic resonance (NMR) experiments,the characteristics of the shale in Chang 7,Shanxi and Benxi Forma-tions are studied,and the pore distributions of these three shales are analyzed. The experimental results show that ① the T2 spectral response of shale presents three types,single peak,two peaks,and three peaks. In this study,the T2 spectrum with two peaks are most developed in shales;② the T2 cut-off values range 0. 49-6. 64 ms with the average value of 1. 57 ms,and the T2 cut-off values for Shanxi shale and Benxi shale can be quickly determined by the peak of the left spectral front;③ the distribution of NMR porosity ranges 0. 55% -10. 26% ,the distribution of NMR mobile fluid percentage ranges 27. 29% - 66. 31% , and the permeability increases with porosity in a power law func-tion;④ the fracture system of Chang 7 shale accounts for 3. 49% -10. 13% ,the fracture proportion for Shanxi shale is 4. 89% -27. 52% ,the fracture proportion for Benxi shale is 2. 97% -8. 18% ,the pores mostly develop in Chang 7 shale,the fractures most richly develop in Shanxi shale,and there are a few large size fractures in some Benxi shales; ⑤ the development effects of Shanxi formation and Benxi Formation are better than that of Chang 7 formation,and Shanxi Formation and Benxi Formation are recommended as the main development layers for shale gas reservoirs in the southeastern Ordos region.