Editing Well logging (section)

====Nuclear magnetic resonance====
{{See also|Nuclear magnetic resonance logging}}
Nuclear magnetic resonance (NMR) logging uses the [[nuclear magnetic resonance|NMR response]] of a [[Formation (stratigraphy)|formation]] to directly determine its [[porosity]] and [[Permeability (earth sciences)|permeability]], providing a continuous record along the length of the [[borehole]].<ref>Gluyas, J. & Swarbrick, R. (2004) Petroleum Geoscience. Publ. Blackwell Publishing</ref><ref name="Kleinberg">Nuclear Magnetic Resonance Imaging – Technology of the 21st century.  Kenyon, Kleinberg, Straley, Gubelin, and Morris. Oilfield Review. http://eps.mcgill.ca/~courses/c550/Literature/NMR-21st-century.pdf{{dead link|date=September 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
The chief application of the NMR tool is to determine moveable fluid volume (BVM) of a rock. This is the pore space excluding clay bound water (CBW) and irreducible water (BVI). Neither of these are moveable in the NMR sense, so these volumes are not easily observed on older logs. On modern tools, both CBW and BVI can often be seen in the signal response after transforming the relaxation curve to the porosity domain. Note that some of the moveable fluids (BVM) in the NMR sense are not actually moveable in the oilfield sense of the word. Residual oil and gas, heavy oil, and bitumen may appear moveable to the NMR precession measurement, but these will not necessarily flow into a well bore.<ref>{{Cite web|url=https://www.spec2000.net/07-nmrlog.htm|title = Crain's Petrophysical Handbook &#124; Login Page}}</ref>