Profiling of Relaxation Time and Diffusivity Distributions with Low Field NMR
Rauschhuber, Michael T.
Hirasaki, George J.
Doctor of Philosophy
Nuclear magnetic resonance (NMR) is a common tool utilized in core analysis. NMR can reveal important information about pore structure, fluid configuration and wettability. However, standard NMR core analysis techniques look at the sample as a whole or only at thin slices. Two NMR pulse sequences are introduced that allow for the determination of relaxation time or diffusion-relaxation time distributions as a function of sample height. One-dimensional T 2 and D-T 2 profiles can be determined with a low-field Maran Ultra spectrometer by implementing nuclear magnetic resonance imaging techniques. Frequency encoding gradients impart spatial resolution to the measurements and allow for the creation of T, and D-T 2 profiles without having to perform multiple slice selective measurements. The first technique, denoted as RARE, relies solely on resolving transverse relaxation, T 2 , as a function of height. The second method, D-T 2 profiling, allows for the determination of both the diffusion coefficient, D, and T 2 as a function of height. The ability to resolve D in addition to T 2 allows fluids with overlapping relaxation times to be distinguished, and therefore it is not necessary to use D 2 O in order to differentiate the water signal from the oil signal. Implementation of these two methods allows for the determination of porosity and saturation profiles. Experiments were performed with a sandpack in order to demonstrate the applicability of these two techniques, and saturation profiles of a sandpack were determined at various stages of the flooding process.
Applied sciences; Relaxation time; Diffusion editing; Low field NMR; Chemical engineering