Dispersion of T_1 and T_2 Nuclear Magnetic Resonance Relaxation in Crude Oils

摘要

Crude oils, which are complex mixtures of hydrocarbons, can be characterized by nuclear magnetic resonace diffusion and relaxation methods to yield physical properties and chemical compositions. In particular, the field dependence, or dispersion, of T_1 relaxation can be used to investigate the presence and dynamics of asphaltenes, the large molecules primarily responsible for the high viscosity in heavy crudes. However, the T_2 relaxation dispersion of crude oils, which provides additional insight when measured alongside T_1, has yet to be investigated systematically. Here we present the field dependence of T_1-T_2 correlations of several crude oils with disparate densities. While asphaltene and resin-containing crude oils exhibit significant T_1 dispersion, minimal T_2 dispersion is seen in all oils. This contrasting behavior between T_1 and T_2 cannot result from random molecular motions, and thus, we attribute our dispersion results to highly correlated molecular dynamics in asphaltene- containing crude oils.