Multi Modal Internal Magnetic Field Gradient Distributions and Single Modal Field Offsets Distributions in Sedimentary Rocks

The internal magnetic field gradient, and field offsets, caused by susceptibility differences at the solid-fluid interfaces, are important features of many MR measurements. Multi modal internal magnetic field gradient distributions are commonly observed in MR experiments with fluid saturated sedimentary rocks. Single modal Lorentzian field offset distributions are also commonly observed in similar systems. In this work, we seek to answer the simple question, how and why are multi modal internal gradient distributions compatible with single modal field offset distributions? T2-Gi measurements of seven samples were undertaken to measure the distribution of internal magnetic field gradients. Simulation based on the distribution of internal magnetic field gradients Gi yields an estimation of the field distribution. The Lorentzian field offset distributions, so calculated agree with the Fourier transformation of the experimental FIDs from the same sample. Single exponential T2* decay was observed in all samples, even those with multi modal internal gradient distributions.