NMR logging exploits the large magnetic moment of hydrogen, which is abundant in rocks in the form of water. The NMR signal amplitude is proportional to the quantity of hydrogen nuclei present in a formation and can be calibrated to give a value for porosity that is free from lithology effects. Uniquely, a petrophysicist can also analyse the rate of decay of the NMR signal amplitude to obtain information on the permeability of the formation - a crucial quantity in hydrocarbon exploration.
Relationship of NMR signal to pore sizeedit
The most important mechanism affecting NMR relaxation is grain-surface relaxation.[2] Molecules in fluids are in constant Brownian motion, diffusing about the pore space and bouncing off the grain surfaces. Upon interaction with the grain surface, hydrogen protons can transfer some nuclear spin energy to the grain (contributing to T1 relaxation) or irreversibley dephase (contributing to T2 relaxation). Therefore the speed of relaxation most significantly depends on how often the hydrogen nuclei collide with the grain surface and this is controlled by the surface-to-volume ratio of the pore in which the nuclei are located. Collisions are less frequent in larger pores, resulting in a slower decay of the NMR signal amplitude and allowing a petrophysicist to understand the distribution of pore sizes.
nuclear, magnetic, resonance, logging, this, article, technical, most, readers, understand, please, help, improve, make, understandable, experts, without, removing, technical, details, february, 2012, learn, when, remove, this, message, nuclear, magnetic, reso. This article may be too technical for most readers to understand Please help improve it to make it understandable to non experts without removing the technical details February 2012 Learn how and when to remove this message Nuclear magnetic resonance NMR logging is a type of well logging that uses the NMR response of a formation to directly determine its porosity and permeability providing a continuous record along the length of the borehole 1 2 Contents 1 Background 2 Relationship of NMR signal to pore size 3 See also 4 ReferencesBackground editNMR logging exploits the large magnetic moment of hydrogen which is abundant in rocks in the form of water The NMR signal amplitude is proportional to the quantity of hydrogen nuclei present in a formation and can be calibrated to give a value for porosity that is free from lithology effects Uniquely a petrophysicist can also analyse the rate of decay of the NMR signal amplitude to obtain information on the permeability of the formation a crucial quantity in hydrocarbon exploration Relationship of NMR signal to pore size editThe most important mechanism affecting NMR relaxation is grain surface relaxation 2 Molecules in fluids are in constant Brownian motion diffusing about the pore space and bouncing off the grain surfaces Upon interaction with the grain surface hydrogen protons can transfer some nuclear spin energy to the grain contributing to T1 relaxation or irreversibley dephase contributing to T2 relaxation Therefore the speed of relaxation most significantly depends on how often the hydrogen nuclei collide with the grain surface and this is controlled by the surface to volume ratio of the pore in which the nuclei are located Collisions are less frequent in larger pores resulting in a slower decay of the NMR signal amplitude and allowing a petrophysicist to understand the distribution of pore sizes See also editNuclear magnetic resonance Nuclear magnetic resonance in porous media Logging while drilling SNMRReferences edit Gluyas J amp Swarbrick R 2004 Petroleum Geoscience Publ Blackwell Publishing a b Nuclear Magnetic Resonance Imaging Technology of the 21st century Kenyon Kleinberg Straley Gubelin and Morris Oilfield Review https www slb com media files oilfield review 08951933 ashx Retrieved from https en wikipedia org w index php title Nuclear magnetic resonance logging amp oldid 1199201070, wikipedia, wiki, book, books, library,
