Shifted Spectrum
Shifted Spectrum :
(n.) Formation Evaluation. A technique in nuclear magnetic resonance (NMR) logging based on the shift in the T2 distributions, or spectra, acquired with different echo spacings. The technique is usually used to detect gas or light oil. These fluids have a significant diffusionrelaxation. A measurement made with a standard short echo spacing will give a signal from these fluids at a certain T2. A measurement made with a long echo spacing will cause more diffusion relaxation and a shorter T2. Other fluids, with minor contribution from diffusion, will not be changed. Gas and light oil can therefore be identified by the shift between the two T2distributions. See: Differential Spectrum, Diffusion Relaxation, Direct Hydrocarbon Typing, Echo Spacing, Nuclear Magnetic Resonance
