The micro-pores present different wettability in shale gas.The organic pores are oil-prone wettability and the inorganic pores are water-prone wettability.Based on the differences of wettability between different pore types of shale

Nuclear Magnetic Resonance (NMR) T

2

spectrum is used to determine the pore size distributions of both organic and inorganic pores.The specific procedures are as follows.Firstly

NMR experiments are performed separately on shale core samples saturated with brine and dodecane respectively to identify T

2

spectra of the organic pore and the inorganic pore.Secondly

joint mercury injection capillary pressure (MICP) and liquid nitrogen adsorption experiments are carried out to establish the quantitative relationship between T

2

and pore-diameter distribution(r

d

=52T

2

).Finally

this formula is used to determine the pore size distribution of organic pore and inorganic pores.These methods are applied to the evaluation of the pore size distribution of the shale gas reservoir in the Silurian Longmaxi Formation in Fuling area

Sichuan Basin.The diameters of organic pores are mainly distributed in the range of 2~50 nm with a peak at 10 nm

and some are in the range of 200~500 nm.The inorganic pores show a wider range of diameter

i.e.2.5 nm~500 nm

with a peak at 50 nm.The micro-cracks show the largest size scale and range from 4 μm to 10 μm in width

with a peak at 5 μm. The pore size distributions derived from NMR coincide with that derived from FIB-SEM quantitative analysis.NMR experiment can measure the whole core and thus can reflect the real in-situ pore size distributions of organic pores and inorganic pores of gas shale.Moreover

the cost of NMR measurement is low

thus demonstrates a good application prospect in gas shale evaluation.