Applications of nuclear magnetic resonance (NMR) logs in shale gas reservoirs for pore size distribution evaluation

Pore size distribution is of extreme important in the shale gas reservoir evaluation and exploration. However, shale is kind of quit complicated material, and traditional well logs (i.e. acoustic, density and neutron) only measure total porosity, while it cannot quantity the different pore size. Also, the laboratory NMR test is not suitable for filed scale well evaluation. Thus, we used NMR well logs to analyze different pore size distribution, we found that relaxation time <4.5ms is the bound fluid volume, which occupied the most part of the total NMR porosity. Furthermore, we also found that another new cutoff (except T₂ cutoff) presence in the T₂ distribution figure. We conclude that such new cutoff is for routine free fluid volume and micro fractures volume. Finally, we found that bound fluid volume is the main part for shale gas storage, and the micro fractures did not contribute a lot.