NMRI methods for characterizing fluid flow in porous media

Abstract

Many important processes such as petroleum production and catalytic chemical reactions involve the flow of fluids through porous media. The measurement of localized velocity can provide information about how fluid is transported in porous media. Furthermore, it provides the possibility of estimating absolute permeability which is an important property used in modeling the flow of fluids in porous media. For many years, there has been a considerable interest by the oil industry and geologists in the measurement and the prediction of flow permeability in rocks. We have investigated the application of Nuclear Magnetic Resonance Imaging to velocity measurement. A stimulated echo pulse field gradient approach was proposed to measure the localized velocity in porous media. The velocity estimation model was derived for the proposed velocity imaging method. Compared to the spin-echo pulsed field gradient method, the proposed method allows longer observation time which is crucial because the relaxation times for fluids in porous media are very small and the NMR signals decay very fast. Furthermore, a narrow pulse approximation concept was applied so that the velocities of spins don't have to be assumed constant during the entire observation time. Preliminary experiments have been carried out to measure velocities for fluid flows inside a cylindrical pipe and glass bead packs. Two dimensional images of the related phase shift values were obtained in arbitrary cross sections with pixel sizes of the order of 0.15 mm 2 . The slice thickness is 5 mm. The data were then analyzed to find the localized velocities. The result showed that the method we proposed is appropriate for measuring the velocities.