Nuclear Magnetic Resonance Logging

Abstract

Nuclear magnetic resonance (NMR), or “nuclear induction” as it was initially called, was developed in the late 1940s (Bloch et al., 1946). Its principle is based on the response of nuclei to magnetic fields (for terminology, see table 2.6.1). Some nuclei, particularly protons — which form the nuclei of hydrogen atoms — have a magnetic moment which can be visualized as a spinning bar magnet. These magnetic moments can be detected with suitable measurement set-ups and an estimation of the location and amount of hydrogens in a sample can be obtained. As hydrogen is abundant in both oil and water, NMR logging was soon proposed for oilfield applications. Chevron developed and patented a NMR logging tool in the 1950s, and in 1960 ran the first NMR log (Brown & Gamson, 1960). One of their primary goals was to quantify the amount of tar in some of their Californian reservoirs. When compared to lighter oils and water, hydrogen atoms in heavy oil take longer to respond to a magnetic field and, conversely, lose an acquired precession faster when the magnetic field is turned off (they “relax” faster). To this day, this represents one of the unique and more interesting applications of NMR logging.