1. n. [Formation Evaluation]
In a nuclear magnetic resonance (NMR) measurement, the loss of coherent energy by hydrogen atoms as they move within the pore space. Hydrogen atoms that move significantly within the pores during a NMR measurement will encounter different magnetic fields and hence will precess at different rates, or dephase. Dephasing contributes only to T2 and is most significant in gas or light oils. The magnitude depends on the field gradient, the echo spacing and the diffusion coefficient of the fluid. Diffusion relaxation can be induced in water by using long echo spacings. This is the basis of the enhanced diffusion technique.