NMR imaging of flow velocity in porous media

Two NMR velocity imaging methods based on the pulsed field gradient stimula ted-echo technique are evaluated for the measurement of fluid flow in porou s media. The spatial resolution and dynamic scale of velocity imaging exper iments are chosen to represent the macroscopic behavior of the complex moti on of fluid molecules. A theoretical formulation for data interpretation is presented and demonstrated with experimental data for water flow in a glas s-bead pack and sandstone samples. Velocity imaging methods investigated in clude the use of flow-induced phase shifts and the measurement of spatially resolved velocity distributions. The results show that the phase-shift met hod is not suitable for some porous media. By contrast, the measurement of spatially resolved velocity distributions not only allows a map of mean vel ocity to be determined, but also provides information about the velocity fi eld within each elemental volume of the image.