NMR Measurements for Gas Adsorption Characterization on Shale: State of the Art and Perspectives

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.