Gas adsorption characterization in
shale is essential
for shale
gas reserve estimation and exploitation. While the adsorption capacity
for containing all the gas in shale nanopores is needed, traditional
volumetric and gravimetric methods can only provide the excess adsorption,
which is smaller and thus needs to be adjusted. NMR relaxometry offers
a new possibility to directly measure the adsorption capacity based
on a relaxation time contrast between the gas inside and the gas outside
the nanoscale pores in the shale. The accuracy of this method has
been validated by comparison with another method combining the volumetric/gravimetric
method and molecular simulation based correction. The current understanding
of the NMR relaxation mechanism of shale gas and the development of
the experimental procedure of this method are introduced here. The
results of related research using these methods are reviewed, and
several future concerns are proposed in the end.