Pore size distributions, pore coupling, and transverse relaxation spectra of porous rocks

The properties of porous rocks make NMR measurements difficult to interpret. Broad distributions of pore sizes give rise to magnetization decays characterized by broad distributions of relaxation times. The pore space, which is well coupled with respect to steady state fluid flow and low frequency electrical conductivity, appears disjoint on time scales probed by NMR. Pulsed field gradient NMR measurements show that pores are elongated and that relaxation times measure the minimum dimension. Diffusion in magnetic field gradients affects the transverse relaxation spectrum in complicated ways, but in the surface dominated regime there is a simple relationship between T1 and T2.