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The influence of solution composition on ÁNHMR relaxation rates by mineral-water interactions in porous sandstones

Proton nuclear magnetic resonance eHNMR) has been used to investigate (1) the relationship between intrinsic penneability (k), a rock physical property, and geochemical characteristics of the pore space in saturated sandstones, represented by the longitudinal relaxation time (T1) of protons in water molecules and (2) molecular dynamics of the mineral surface-solute-water system in the pore environment. Variations in log(T12)/log(k) with solution composition indicate that T 1 in saturated rock cores is correlated with permeability. The consideration of flow porosity does not improve this relationship, as illustrated by relations between log(<PFT12)/log(k) and solution composition. The key to the T 1-k relationship is changes in solution viscosity due to mineral surface-solution interactions. The longitudinal relaxation rate (R 1 = i 1 ) Increases In bulk solutions of . NaC1<LiC1<CaCI2<MgCI2 (ordered by increasing effect) and decreases slightly in KCI solutions. These effects are due to variations in solution viscosity, which directly influences R1 through its effects on correlation time. Contributions to R1 from the mineral-water interface and solute ions vary with solution composition. The contribution from the interface is dominant at MgCl2 and KCI concentrations <0.1-0.4 m (surface regime), but at higher concentrations, solute ions interact with the interface to alter the surface's contribution to relaxation (surface/solute regime). The boundary between the two regimes depends upon how strongly the mineral surface contributes to R l' Regime boundaries of the Berea and Red Orthoquartzite