The Effects of Field Strength on NMR Measurements

There is a growing interest in oil and gas exploration in unconventional materials such as shales. This has lead to a need for increased sensitivity in NMR measurements on such materials because of their low porosities and consequent low NMR signal levels.

The most direct way to increase sensitivity is to increase the operating frequency of the NMR instruments, so we now offer GeoSpec models operating at 2, 12 and 23 MHz. However, NMR measurements made at different frequencies are not directly comparable, so the user needs to be aware of the differences when comparing samples measured at different frequencies. 

For example, as well as improving signal to noise ratios, measurements at higher field make short T₂ values easier to detect which can result in higher effective porosity values. Higher frequencies also allow better resolution of on- and off-axis peaks in 2D data maps, making fluid typing and detection of organic material such as kerogen and bitumen easier.

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