Abstract: Spin relaxation time measurement is one of the most important applications of NMR technology. Relaxation parameters derived from NMR measurements provide structural and dynamic information of molecules. Applications in porous media further show that the distribution of relaxation time can be use to determine pore size, irreducible water saturation, and formation permeability etc. In this paper we described three relaxation mechanisms and how they can be used to obtain information about rock porous media. Bulk relaxation time of free-fluid is used to differentiate the type of fluids and the quality of oil, surface relaxation distribution provides information of pore size and capillary bonding, and diffusion coefficient improves the capability of fluid typing and pore geometry determination. We also summarized various methods for measuring relaxation times and selfdiffusion coefficient, as well as their distributions.

Key words: NMR, relaxation mechanism, rock porous media, relaxation time, diffusion coefficient