Relaxation Analysis of Porous Media at High Magnetic Field Strengths: The Influence of Internal Gradients

Abstract

The strengths of surface interaction in catalytic materials or wettability in oil‐field reservoir rocks can be assessed based on the ratio of nuclear magnetic resonance (NMR) relaxation times T1/T2. It is often desirable to measure these relaxation times at intermediate or high magnetic field strengths (B0⩾1 T) in order to retain chemical shift information and improve the signal‐to‐noise ratio. However, T2 relaxation is influenced by diffusion through internal magnetic field gradients. These internal gradients, caused by the magnetic susceptibility contrast between liquid and solid, scale with increasing field strength and result in the observation of an effective T2,eff relaxation time. Here, we discuss a method by which the “true” surface relaxivity dominated T2 can be recovered using the example of materials relevant to liquid‐phase catalysis. This method extends the range of magnetic field strengths available for use in porous media studies. We consider the use of T2,eff—T2,eff exchange experiments as an alternative probe of pore size in high‐field relaxation analysis of oil reservoir rocks. We also show prelilminary results from a NMR grain size measurement utilizing Bayesian analysis of single point imaging k‐space data.