Understanding Relationships Between NMR and Pore Size Distributions in Porous Media

Conventional wisdom for NMR interpretations of water-saturated porous media is that the NMR spectra are analogous to the pore size distribution of the system. This is the basis for understanding porous media as containing large vs. small pores, and is used as a justification for NMR-based permeability correlations. However, there are cases whereby issues of poor connectivity between pores can skew the NMR T2 distribution such that it may no longer be representative of the pore sizes present in the core. This in turn can lead to errors in characterization of a given porous medium. This work investigates this potential problem by constructing a digital rock model and performing pore-level simulations in order to generate the corresponding NMR pore size distribution for this system. The same physical pore size distribution is maintained, but the connectivity is reduced between the different pores, and the corresponding shifts in the NMR distribution are observed.