Magnetic Resonance Imaging with a Variable Field Superconducting Magnet that can be rotated for Vertical or Horizontal Operation

Sarah Vashaee, Ming Li, Bryce MacMillan, Razieh Enjilela, Derrick Greem, Florin Marica, Bruce Balcom

Research output: Chapter in Book/Conference paperConference paper

Abstract

Magnetic Resonance (MR) is widely employed in the petroleum industry for down-hole logging and for laboratory core analysis. Sensitivity of the magnetic resonance experiment to fluid type and fluid environment makes it uniquely well suited to these applications. The same advantages should accrue to Magnetic Resonance Imaging (MRI) measurements of core flooding experiments. The ability of MRI to directly measure fluid saturation and fluid environment in three dimensions, as a function of time, has to this point, not been fully realized for core flood applications. Bulk 1H relaxation time measurements are near universally undertaken at low magnetic field to reduce magnetic susceptibility mismatch effects. These fields, typically 0.05 Tesla (2 MHz for 1H), are too low for MRI studies. Higher magnetic fields (3 Tesla and above) are commonly employed for biomedical MRI studies with superconducting magnets.
Susceptibility mismatch effects at these field strengths can be severe for many core plug samples and these higher field are generally inappropriate for rock core studies. What is the best field for petroleum core plug MRI studies? It will be sample dependent as one seeks to balance greater sensitivity at high field with susceptibility effects which decrease the transverse signal lifetimes (T2 and T2*) as field increases. New generation superconducting magnets, actively cooled rather than passively cooled, are permanently connected to the magnet power supply and thus have the possibility of variable field operation. We have recently installed a variable field superconducting magnet MRI instrument which permits operation in the field range 0.01 Tesla to 3 Tesla. This magnet permits one to maximize the sample magnetization for high sensitivity core flooding MRI measurements, while controlling the effect of susceptibility mismatch on the
signal lifetime. Because of the elimination of liquid cryogens the new magnet is a fraction of the size and weight of conventional superconducting magnets. The magnet can easily be rotated, from horizontal to vertical, by one person.
SCA2017-024 2/12 Variable field operation permits MRI measurement of other nuclei of interest and importance in core flooding studies. The gyromagnetic ratio of sodium 23Na and fluorine 19F are each less than that of hydrogen 1H but one may increase the static field strength to compensate for the decrease in gyromagnetic ratio such that the RF probe employed to excite and detect the MRI signal has an unchanged frequency. This provides the experimentalist an entirely new way to undertake multi-nuclear MRI studies of core plug systems.
Original languageEnglish
Title of host publicationInternational Symposium of the Society of Core Analysts held in Vienna, Austria, 28 August-1 September 2017
Place of PublicationAustria
PublisherSociety of Core Analysts
Number of pages12
Publication statusPublished - 2017
Externally publishedYes
Event2017 International Symposium of the Society of Core Analysts - Vienna, Austria
Duration: 28 Aug 20171 Sep 2017

Conference

Conference2017 International Symposium of the Society of Core Analysts
CountryAustria
CityVienna
Period28/08/171/09/17

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