MAGNETIZATION EVOLUTION IN CONNECTED PORE SYSTEMS .2. PULSED-FIELD-GRADIENT NMR AND PORE-SPACE GEOMETRY

The time evolution of nuclear magnetization in a porous medium, e.g., proton dipole moments on water saturating a sandstone, can be describe d in terms of relaxation-operator eigenstates (modes of the magnetizat ion). Decay of the magnetization in a pulsed-field-gradient NMR (PFGNM R) or stimulated-echo experiment is described by the intermediate scat tering function (ISF). The ISF is a sensitive probe of the spatial str ucture of the modes of the magnetization. We have studied the time evo lution of the magnetization and the behavior of the ISF by solving the relaxation-operator problem. A suitable set of PFGNMR measurements pr ovides important information about the pore-space geometry, for exampl e, the gradient-independent part of the spectrum of decay rates is con tributed by large or isolated pores.