Determination of filter cake properties by nuclear magnetic resonance

Low resolution nuclear magnetic resonance (NMR) is used to investigate the porosity and permeability of filter cakes. Porosity is determined by free induction decay measurements of the fully saturated packings. NMR spin-lattice and spin-spin relaxation measurements were performed on the samples. It is shown that the permeability of the packed beds correlates strongly with the three material parameters of the sample: porosity a and the relaxation time constants T-1 and T-2. All three parameters can be determined with a low resolution NMR spectrometer. Validation of the approach is achieved from flow experiments and analytical determination of porosity and permeability. After calibration, the new method allows an easy and rapid determination of filter cake properties under different process conditions. Changes of porosity and permeability of the filter cake during processing can be studied systematically. Filtration problems, such as compressibility of the filter cake or migration of small particles plugging the filter cake, can be analyzed with this method.