Pore Size Distributions and Hydraulic Conductivity of Rocks Derived from Magnetic Resonance Sounding Relaxation Data

In Magnetic Resonance Sounding (MRS) the hydrogen protons in the pore water are excited with an artificial magnetic field. This excitation field is usually generated by a circular/square or figure-of-eight antenna loop energized by an alternating current which oscillated with the local Larmor frequency of the hydrogen protons. The amplitudes and of relaxation constants of MRS signals are directly linked to the amount of pore fluid (e.g. water content) and the pore sizes in the subsurface. The fluid phase within the pore space exhibits well defined relaxation rates governing the decay of the nuclear magnetisation of the excited protons within a specific pore size, and thus can be correlated with the hydraulic permeability K of the material. Hydrological models using grain size analysis and NMR models using pore sizes are integrated and general relations between observed MRS decay times and derived hydraulic permeability K are reviewed and discussed and an in-situ K-estimation template is introduced.